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This guideline is a part of the English Wikipedia's Manual of Style. Editors should follow it, except where common sense and the occasional exception will improve an article. Before editing this page, please make sure that your revision reflects consensus.

Shortcuts: WP:MOSNUM WP:DATE MOS:DATE MOS:NUM

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This part of the Manual of Style aims to achieve consistency in the use and formatting of dates and numbers in Wikipedia articles. Consistent standards make articles easier to read, write and edit. Where this manual provides options, consistency should be maintained within an article, unless there is a good reason to do otherwise. In direct quotations, the original text should be preserved.

In June 2005, the Arbitration Committee stated that when either of two styles is acceptable, it is inappropriate for an editor to change an article from one to the other without substantial reason. For example, with respect to British date formats as opposed to American it would be acceptable to change from American format to British if the article concerned a British subject. Edit warring over optional styles (such as 14 February and February 14) is unacceptable. If an article has been stable in a given style, it should not be converted without a style-independent reason. Where in doubt, defer to the style used by the first major contributor.

Non-breaking spaces

See also: Wikipedia:Line break handling and Wikipedia:Manual of Style#Non-breaking spaces

• Wikipedia recommends the use of a non-breaking space (also known as a hard space) when necessary to prevent the end-of-line displacement of elements that would be awkward at the beginning of a new line:
  • in compound expressions in which figures and abbreviations or symbols are separated by a space (17 kg, AD 565, 2:50 pm);
  • on the left side of spaced en dashes, if necessary for comprehension; and
  • in other places where displacement might be disruptive to the reader, such as £11 billion, 5° 24′ 21.12″ N, Boeing 747, and the first two items in 7 World Trade Center.
• A hard space can be produced with the HTML code   instead of the space bar: 19 kg yields a non-breaking 19 kg.
• A literal hard space should not be used since some browsers will not load them properly when editing.
• Hard spaces can also be produced by using the {{nowrap}} template: {{nowrap|8 sq ft}} produces a non-breaking 8 sq ft. This is especially useful for short constructions requiring two or more hard spaces, as in the preceding example. Template {{nowrap}} has the disadvantage that if the enclosed text starts or ends with a space, these spaces are forced outside in the resulting HTML, and unpredicted breaks may occur. If   occurs right before {{nowrap}}, or at the start of text within {{nowrap}}, some browsers allow a break at that point.
• In some older browsers, quotation marks separated by a hard space are broken at the end of a line: ("She said 'Yes!' ").
• Unlike normal spaces, multiple hard spaces are not compressed by browsers into a single space.

Chronological items

Precise language

See also: Wikipedia:As of

Avoid statements that will date quickly, except on pages that are regularly updated, such as those that cover current events. Avoid such items as now and soon (unless their intended meaning is clear), currently and recently (except on rare occasions where they are not redundant), or phrases such as in modern times and the sixties. Instead, when writing about past events use more precise phrases such as during the 1990s, or in August 1969. For future and current events use phrases such as as of March 2007, or since the start of 2005 which indicate the time-dependence of the information to the reader.

To assist editors in keeping the information up to date, statements about future and current events may be used in conjunction with the "as of" technique. This is done using the {{as of}} template to tag information that may become dated quickly: {{as of|2008}} produces the text As of 2008 and categorises the article appropriately. However, this technique is not an alternative to using precise language.

Time of day

Context determines whether the 12- or 24-hour clock is used; in both, colons separate hours, minutes and seconds (1:38:09 pm and 13:38:09).

• 12-hour clock times end with dotted or undotted lower-case a.m. or p.m., or am or pm, which are spaced (2:30 p.m. or 2:30 pm, not 2:30p.m. or 2:30pm). Noon and midnight are used rather than 12 pm and 12 am; whether midnight refers to the start or the end of a date will need to be specified unless this is clear from the context.
• 24-hour clock times have no a.m., p.m., noon or midnight suffix. Discretion may be used as to whether the hour has a leading zero (08:15 or 8:15). 00:00 refers to midnight at the start of a date, 12:00 to noon, and 24:00 to midnight at the end of a date but should not be used for the first hour of the next day e.g. use 00:10 for ten minutes after midnight.

Time of day is normally expressed in figures rather than being spelled-out. For further information and information on time intervals (e.g. 5 minutes) see the "Numbers as figures or words" section.

Day, month and season names

See Wikipedia:Manual of Style (capital letters)#Calendar items

Dates

• Wikipedia does not use ordinal suffixes, articles, or leading zeros. Wikipedia does not insert a comma between month and year; however, a comma is required between day and year.

Incorrect	Correct
9th May the 9th of May	9 May
May 9th	May 9
May, 2001	May 2001
9 May, 2001 09 May 2001	9 May 2001
May 9 2001 May 09, 2001	May 9, 2001

• If a date range is abbreviated, use the formats 5–7 January 1979 or January 5–7, 2002, with an unspaced en-dash.
• A night may be expressed in terms of the two contiguous dates using a slash (the bombing raids of the night of 30/31 May 1942).
• Yearless dates (5 March, March 5) are inappropriate unless the year is obvious from the context. There is no such ambiguity with recurring events, such as "January 1 is New Year's Day".
• YYYY-MM-DD style dates (1976-05-31) are uncommon in English prose, and should not be used within sentences. However, they may be useful in long lists and tables for conciseness. (If the only purpose why they are used in a particular table is ease of comparison, consider using {{sort|2008-11-01|1 November 2008}}.) Because some perceive dates in that style to be in conformance with the current ISO 8601 standard, that format should never be used for a date that is not in the (proleptic) Gregorian calendar, nor for any year outside the range 1583 through 9999.

Full date formatting

In general, the following formats are acceptable:

• Month before day: February 14 and February 14, 1990 (comma required)
• Day before month: 14 February and 14 February 1990

Date formatting in an article is governed by the following three guidelines.

Format consistency

• Dates in article body text should all have the same format.
• Dates in article references should all have the same format.

These requirements apply to dates in general prose and reference citations, but not to dates in quotations or titles.

Strong national ties to a topic

• Articles on topics with strong ties to a particular English-speaking country should generally use the more common date format for that nation. For the U.S. this is month before day; for most others it is day before month. Articles related to Canada may use either format consistently.
• In certain subject areas the customary format may differ from the usual national one: for example, articles on the modern U.S. military often use day before month, in accordance with usage in that field.

Retaining the existing format

• If an article has evolved using predominantly one format, the whole article should conform to it, unless there are reasons for changing it based on strong national ties to the topic.
• In the early stages of writing an article, the date format chosen by the first major contributor to the article should be used, unless there is reason to change it based on strong national ties to the topic. Where an article that is not a stub shows no clear sign of which format is used, the first person to insert a date is equivalent to "the first major contributor".

Dates of birth and death

At the start of an article on an individual, his or her dates of birth and death are provided. For example: "Charles Darwin (12 February 1809 – 19 April 1882) was a British ..."

• For an individual still living: "Serena Williams (born September 26, 1981) ...", not "... (September 26, 1981 –) ..."
• When only the years are known: "Socrates (470–399 BC) was..."
• When the year of birth is completely unknown, it should be extrapolated from earliest known period of activity: "Offa of Mercia (before 734 – 26 July 796) ..."
• When the year of birth is known only approximately: "Genghis Khan (c. 1162 – August 18, 1227) ..."
• When the years of both birth and death are known only approximately: "Dionysius Exiguus (c. 470 – c. 540) ..."
• When the year of death is completely unknown, it should be extrapolated from last known period of activity: "Robert Menli Lyon (1789 – after 1863) ..."
• When the reign of a sovereign is uncertain: "Rameses III (reigned c. 1180 BCE – c. 1150 BCE) ..."
• When the individual is known to have been alive (flourishing) at certain dates, [[floruit|fl.]] is used to link to floruit, in case the meaning is not familiar: "Osmund (fl. 760–772) ..."
• When the individual is known to have been alive as early as about 660, and to have died in 685: "Aethelwalh (fl. c. 660–685) ..."
• Locations of birth and death are given subsequently rather than being entangled with the dates.

In biographical infobox templates, provide age calculation with {{birth date and age}} for living people and {{death date and age}} for the deceased when the full birth or death date, respectively, is known. (However, avoid these templates unless both dates are in the Gregorian calendar, due to possibly inaccurate calculations if the birth date is Julian and the death date is Gregorian, or the end of a Julian century intervenes.)

Other date ranges

Dates that are given as ranges should follow the same patterns as given above for birth and death dates. Ranges that come up to the present (as of the time that the information was added to the article) should generally be given in ways that prevent their becoming counterfactually obsolete, e.g. from 1996 onward (as of October 2007), not from 1996 to the present; "the present" is a constantly moving target. In the main text of articles, the form 1996– (with no date after the en-dash) should not be used, though it is preferred in infoboxes and other crowded templates or lists, with the caveat that they may need to be examined by editors more frequently to see if they need to be updated; it is helpful to other editors to add an HTML comment immediately after such constructions, giving the as-of date, e.g.: <!--as of 10 October 2007-->. The form since 1996 should be used in favor of 1996–present in article text and infoboxes.

Linking and autoformatting of dates

This section is the subject of a current discussion on the talk page. Please feel free to join in. This doesn't mean that you may not be bold in editing this section, but it can't hurt to check the discussion first.

• Linking: Dates (years, months, day and month, full dates) should not be linked, unless there is a reason to do so. More information can be found at WP:CONTEXT#Dates.
• Autoformatting: Dates should not be linked purely for the purpose of autoformatting (even though in the past this was considered desirable).¹

Longer periods

• Shortcut: WP:MONTH

  Months are expressed as whole words (February, not 2), except in the ISO 8601 format; months (and days of the week) are proper nouns, and therefore capitalized. Abbreviations such as Feb are used only where space is extremely limited, such as in tables and infoboxes. Do not insert of between a month and a year (April 2000, not April of 2000).

• Shortcut: WP:SEASON

  Seasons. Because the seasons are not simply reversed in each hemisphere – and areas near the equator tend to have just wet and dry seasons – neutral wording may be preferable (in early 1990, in the second quarter of 2003, around September). Use a date or month rather than a season name, unless there is a logical connection (the autumn harvest). Seasons are normally spelled with a lower-case initial.

• Shortcut: WP:YEAR

  Years

• Years are normally expressed in digits. Avoid inserting the words the year before the digits (1995, not the year 1995), unless the meaning would otherwise be unclear.
• Year ranges, like all ranges, are separated by an en dash, not a hyphen or slash (2005–08, not 2005-08 or 2005/08). A closing CE/AD year is normally written with two digits (1881–86) unless it is in a different century from that of the opening year (1881–1986). The full closing year is acceptable, but abbreviating it to a single digit (1881–6) or three digits (1881–886) is not. A closing BCE or BC year is given in full (2590–2550 BCE). While one era signifier at the end of a date range requires an unspaced en dash (12–5 BC), a spaced en dash is required when a signifier is used after the opening and closing years (5 BC – AD 29).
• A slash may be used to indicate regular defined yearly periods that do not coincide with calendar years (the financial year 1993/94, the 1999/2000 snooker season).
• To indicate around/approximately/about, the abbreviations c. and ca. are preferred over circa, approximately or approx., and are spaced (c. 1291). Do not use a question mark for this function (1291?), as this may imply to the reader an uncertainty on the part of Wikipedia editors rather than on the part of reliable historians.

• Shortcut: WP:DECADE

  Decades
  • Decades as such contain no apostrophe (the 1980s, not the 1980's). The two-digit form is never used in reference to the decade as a time span per se.
  • The two-digit style, to which a preceding apostrophe is typically added, is used only in reference to a social era or cultural phenomenon that roughly corresponds to and is said to define a decade, and only if it is used in a sourceable stock phrase (the Roaring '20s, the Gay '90s), or when there is a notable connection between the period and what is being discussed in the sentence (a sense of social justice informed by '60s counterculture, but grew up in 1960s Boston, moving to Dallas in 1971). Such an abbreviation should not be used if it would be redundant ('80s Reaganomics) or if it does not have a clear cultural significance and usage (the '10s).

• Shortcuts: WP:CENTURY WP:MILLENNIUM

  Centuries and millennia
  • There was no year 0. Therefore, for dates AD (or CE) the 1st century was 1–100, the 17th century was 1601–1700, and the second millennium was 1001–2000; for dates BC (or BCE) the 1st century was 100–1; the 17th century was 1700–1601, and the second millennium was 2000–1001.
  • Do not capitalize century or millennium unless other circumstances require it.
  • Forms such as the 1700s are normally best avoided (although the difference in meaning should be noted: the 1700s is 1700–1799, whereas the 18th century is 1701–1800).

Year numbering systems

• Either CE and BCE or AD and BC can be used—spaced, undotted (without periods) and upper-case. Choose either the BC/AD or the BCE/CE system, but not both in the same article. Style guides generally recommend writing AD before a year (AD 1066) and after a century (2nd century AD); however, writing AD after the year (1066 AD) is also common in practice. The other abbreviations always appear after (1066 CE, 3700 BCE, 3700 BC). The absence of such an abbreviation indicates the default, CE/AD. It is inappropriate for a Wikipedia editor to change from one style to another unless there is a substantive reason; the Manual of Style favors neither system over the other.
• Uncalibrated (bce) radiocarbon dates: Some source materials will indicate whether a date is calibrated or not simply by a change in capitalization; this is often a source of confusion for the unwary reader. Do not give uncalibrated radiocarbon dates (represented by the lower-case bce unit, occasionally bc or b.c. in some sources), except in directly quoted material, and even then include a footnote, a [square-bracketed editor's note], or other indication to the reader what the calibrated date is, or at least that the date is uncalibrated. Calibrated and uncalibrated dates can diverge surprisingly widely, and the average reader does not recognize the distinction between bce and BCE / BC.
• Abbreviations indicating long periods of time ago—such as BP (before present), as well as various annum-based units such as ka (kiloannum), Ma (megaannum) and Ga (gigaannum) are given as full words on first occurrence. Where source quotations use the abbreviations kya (thousand years ago), mya (million years ago), or bya (billion years ago) this should be explained to the reader, as in "a measured Libby radiocarbon date of 35.1 mya" (million years ago, or 35.1 Ma) had to be calibrated against then newly available stratigraphic dating references in order to estimate a Cambridge standardized date of 36.2 Ma BP cal. The kya, mya and bya symbols are deprecated in some fields such as geophysics and geology, but remain common in others, such as anthropology.

• BP: Do not convert other notations to BP unless you are certain of what you are doing. In some contexts the unit BP is actually defined as "years before January 1, 1950", not "years before the literal present", and the conversion may introduce an error if the date being converted is not a wide approximation (18,000 BP) but a more narrow one or an actual known year. BP years are given as 18,000 BP or spelled out as 18,000 years before present (not 18,000 YBP, 18,000 before present, 18,000 years before the present, or similar.)

Calendars

See also: Old Style and New Style dates

Dates can be given in any appropriate calendar, as long as the date in either the Julian or Gregorian calendars is provided, as described below. For example, an article on the early history of Islam may give dates in both Islamic and Julian calendars. Where a calendar other than the Julian or Gregorian is used, this must be clear to readers.

• Current events are given in the Gregorian calendar.
• Dates before the adoption of the Gregorian calendar on 15 October 1582 are normally given in the Julian calendar. The Julian day and month should not be converted to the Gregorian calendar, but the start of the Julian year should be assumed to be 1 January (see below for more details).
• Dates for Roman history before 45 BC are given in the Roman calendar, which was neither Julian nor Gregorian. When (rarely) the Julian equivalent is certain, it may be included.
• The Julian or Gregorian equivalent of dates in early Egyptian and Mesopotamian history is often debatable. Follow the consensus of reliable sources, or indicate their divergence.
• Dates of events in countries using the Gregorian calendar are given in the Gregorian calendar. This includes some of the Continent of Europe from 1582, the British Empire from 14 September 1752, and Russia from 14 February 1918 (see the Gregorian calendar article).

The dating method used in a Wikipedia article should follow that used by reliable secondary sources. If the reliable secondary sources disagree, choose the most common used by reliable secondary sources and note the usage in a footnote.

At some places and times, dates other than 1 January were used as the start of the year. The most common English-language convention was the Annunciation Style used in Britain and its colonies, in which the year started on 25 March, Annunciation Day; see the New Year article for a list of other styles. 1 January is assumed to be the opening date for years; if there is reason to use another start-date, this should be stated.

If there is a need to mention Old Style or New Style dates in an article (as in the Glorious Revolution), a footnote should be provided on the first usage, stating whether the "New Style" refers to a start of year adjustment or to the Gregorian calendar (it can mean either).

Time zones

When writing a date, first consider where the event happened and use the time zone there. For example, the date of the Attack on Pearl Harbor should be December 7, 1941 (Hawaii time/date). If it is difficult to judge where, consider what is significant. For example, if a vandal based in Japan attacked a Pentagon computer in the US, use the time zone for the Pentagon, where the attack had its effect. If known, include the UTC date and time of the event in the article, indicating that it is UTC.

Numbers

Numbers as figures or words

As a general rule, in the body of an article, single-digit whole numbers from zero to nine are spelled out in words; numbers greater than nine are commonly rendered in numerals, or may be rendered in words if they are expressed in one or two words (16 or sixteen, 84 or eighty-four, 200 or two hundred, but 3.75, 544, 21 million). This applies to ordinal numbers as well as cardinal numbers. However there are frequent exceptions to these rules.

• In tables and infoboxes, quantitative data is expressed as numerals; numerals will also fit better in limited space. Numbers within a table's explanatory text and comments should be consistent with the general rule.
• Comparable quantities should be all spelled out or all figures: we may write either 5 cats and 32 dogs or five cats and thirty-two dogs, not five cats and 32 dogs.
• Adjacent quantities which are not comparable should usually be in different formats: twelve 90-minute volumes or 12 ninety-minute volumes is more readable than 12 90-minute volumes or twelve ninety-minute volumes.

• Numbers that begin a sentence are spelled out, since using figures risks the period being read as a decimal point or abbreviation mark; it is often better to recast the sentence than to simply change format, which may produce other problems: do not use Nineteen forty five and 1950 were important elections for the Labour Party, but recast, for example: The elections of 1945 and 1950 were important for the Labour Party.

• The numerical elements of dates and times are not normally spelled out (that is, do not use the seventh of January or twelve forty-five p.m. or Two thousand eight was the year that ... ). However, they should be spelled out where customary in historical references such as Seventh of March Speech and Fifth of November; these are treated as proper names.
• Centuries are named in figures: (the 5th century CE; 19th-century painting); when the adjective is hyphenated, consider nineteenth-century painting, but not when contrasted with painting in the 20th century.

• Simple fractions are normally spelled out; use the fraction form if they occur in a percentage or with an abbreviated unit (⅛ mm or an eighth of a millimeter, but never an eighth of a mm) or if they are mixed with whole numerals.
• Decimal representations containing a decimal point are not spelled out (1.00, 3.14159).
• Numbers in mathematical formulae are never spelled out (3 < π < 22/7, not three < π < 22 sevenths).
• Measurements, stock prices, and the like, are normally stated in figures, even when the value is a small positive integer: 9 mm, The option price fell to 5 within three hours after the announcement.

• The use of words rather than figures may be preferred when expressing approximate numbers; for example one hundred thousand troops may be preferable to 100,000 troops when the size of the force is not known exactly.

• Sometimes figures and words may carry different meanings, for example Every number except one implies that there is one exception (we don't know which), while Every number except 1 means that the specific number 1 is the exception.
• Proper names, formal numerical designations, and other idioms comply with common usage (Chanel No. 5, 4 Main Street, 1-Naphthylamine, Channel 6). This is the case even where it causes a numeral to open a sentence, although this is usually avoided by rewording.
• Most proper names containing numbers spell them out (e.g. Fourth Amendment, Seventeenth Judicial District, Seven Years' War); the proper names of military units do not.

Typography

• Spelled-out two-word numbers from 21 to 99 are hyphenated (fifty-six), as are fractions (seven-eighths). Do not hyphenate other multi-word numbers (five hundred, not five-hundred).
• Where a whole number in a percentage is spelled out, the percent sign is not used (three percent or 3%, not three %).
• The ordinal suffix (e.g., th) is not superscripted (23rd and 496th, not 23^rd and 496^th).

Large numbers

See also: Order of magnitude and Long and short scales

• In large numbers (i.e., in numbers greater than or equal to 10,000), commas are generally used to break the sequence every three places left of the decimal point, e.g. "8,274,527". In scientific context, thin spaces can also be used (but using {{nowrap}} to prevent line-breaking within numbers), e.g. "8 274 527" ({{nowrap|8 274 527}}, or using the thin space character instead of its HTML entity). Consistency within an article is desirable as always.
• Large round numbers are generally assumed to be approximations; only where the approximation could be misleading is it necessary to qualify with about or a similar term.
• Avoid overly precise values where they are unlikely to be stable or accurate, or where the precision is unnecessary in the context (The speed of light in a vacuum is 299 792 458 metres per second may well be appropriate – for one thing, the metre is now defined by that relation; The distance from the Earth to the Sun is 149 014 769 kilometres and The population of Cape Town is 2,968,790 would usually not be, because both values are unstable at that level of precision, and readers are unlikely to care in the context.)
• Scientific notation (5.8×10⁷) is preferred in scientific contexts. This should use the {{e}} template, for example ''5.8{{e|7}}''.
• Where values in the millions occur a number of times through an article, upper-case M may be used for million, unspaced, after spelling out the first occurrence. (She bequeathed her fortune of £100 million unequally: her eldest daughter received £70M, her husband £18M, and her three sons £4M each.)
• Billion is understood as ×10⁹ (short scale). After the first occurrence in an article, billion may be abbreviated to unspaced bn ($35bn). Where the alternative meaning 10¹² (long scale) is required for some reason, a footnote or inline comment is appropriate. Except in computing and certain scientific contexts, giga- or its symbol G is inappropriate.

Fractions

The template {{frac}} is available for representing common fractions. For ^p⁄_q, type {{frac|p|q}}. For N+^p⁄_q, type {{frac|N|p|q}}. When copied and pasted, the latter text will appear as N+p/q.

Decimal points

• A decimal point is used between the integer and the fractional parts of a decimal; a comma is never used in this role (6.57, not 6,57).
• The number of decimal places should be consistent within a list or context (The response rates were 41.0 and 47.4 percent, respectively, not The response rates were 41 and 47.4 percent, respectively).
• Numbers between negative one and positive one require a leading zero (0.02, not .02); exceptions are sporting performance averages (.430 batting average) and commonly used terms such as .22 caliber.
• For numbers with more than four digits after the decimal point, these can be separated in groups of three by thin spaces protected by {{nowrap}}, or with {{val}}, which obtains the same appearance using margins instead of thin space characters. (An exception is that a single digit at the end would not have a preceding space; {{val}} handles this automatically, e.g. "0.1234567".) Optionally, truncated representations of mathematically defined constants with fifteen or more digits after the point can use groups of five digits (e.g. "e = 2.71828 18284 59045…"); in this case, the number of digits used between the point and the ellipsis, being arbitrary, should be a multiple of five (or of three, if three-digit groups are used). Note that {{val}} can fail to correctly handle numbers with too many significant digits.

Percentages

• Percent or per cent are commonly used to indicate percentages in the body of an article. The symbol % is more common in scientific or technical articles and in complex listings.
• The symbol is unspaced (71%, not 71 %).
• In tables and infoboxes, the symbol % is normally preferred to the spelled-out percent or per cent.
• Ranges are preferably formatted with one rather than two percentage signifiers (22–28%, not 22%–28%).
• Avoid ambiguity in expressing a change of rates. This can be done by using percentage points, not percentages, to express a change in a percentage or the difference between two percentages; for example, "The agent raised the commission by five percentage points, from 10 to 15%" (if the 10% commission had instead been raised by 5%, the new rate would have been 10.5%). It is often possible to recast the sentence to avoid the ambiguity ("made the commission larger by half."). Percentage point should not be confused with basis point, which is a hundredth of a percentage point.

Natural numbers

The set of natural numbers has two common meanings: {0,1,2,3,…}, which may also be called non-negative integers, and {1,2,3,…}, which may also be called positive integers. Use the sense appropriate to the field to which the subject of the article belongs if the field has a preferred convention. If the sense is unclear, and if it is important whether or not zero is included, consider using one of the alternative phrases rather than natural numbers if the context permits.

Repeating decimals

The preferred way to indicate a repeating decimal is to place a bar over the digits that repeat. To achieve this the template {{overline}} can be used. For example, the markup 14.{{overline|285714}} gives "14.285714".

Consider a short explanation of the notation the first time this notation is used in an article. Some authors place the repeating digits in parentheses rather than using an overbar (perhaps because overbars are not available in their typesetting environment) but this should be avoided in Wikipedia to avoid confusion with expressing uncertainty.

Non-base-10 notations

For numbers expressed in bases other than base ten:

• In computer-related articles, use the C programming language prefixes 0x (zero-ex) for hexadecimal and 0 (zero) for octal. For binary, use 0b. Consider including a note at the top of the page about these prefixes.
• In all other articles, use subscript notation. For example: 137₉, 241₆, 2A9₁₂, A87D₁₆ (use <sub> and </sub>).
• For base eleven and higher, use whatever symbols are conventional for that base. One quite common convention, especially for base 16, is to use upper-case A–F for digits from 10 through 15 (0x5AB3).

Scientific notation, engineering notation, and uncertainty

Notations

• Scientific notation is done in the format of 1 leading digit/decimal marker/rest of digits/×10ⁿ, where n is the integer that gives one leading digit.

• 1.602×10⁻¹⁹ is a proper use of scientific notation.
• 160.2×10⁻¹⁷ is not a proper use of scientific notation.

• Engineering notation is done in the format of leading digits/decimal marker/rest of digits/×10ⁿ, where n is a multiple of 3. The number of leading digits is adjusted accordingly.

• 132.23×10⁶ is a proper use of engineering notation.
• 1.3223×10⁸ is a not proper use of engineering notation.

• When using either scientific or engineering notation in articles, consistency is preferred (e.g., do not write A 2.23×10² m region covered by 234×10⁶ grains of sand).
• Use discretion when it comes to using scientific and engineering notation. Not all values need to be written in it (e.g., do not write the house was 1.25×10² y old, but rather the house was 125 years old in 2008 or simply the house was built in 1883).

• Sometimes it is useful to compare values with the same power of 10 (often in tables) and scientific or engineering notation might not be appropriate.

Uncertainty

• Uncertainties can be written in various ways:
  • Value/±/uncertainty/×/10ⁿ/unit symbol (e.g., 1.534±0.35×10²³ m)
    • Do not group value and uncertainty in parenthesis before the multiplier (e.g., do not write (15.34 ± 0.35) × 10²³ m)
  • Value/superscript positive uncertainty/subscript negative uncertainty/×/10ⁿ/unit symbol (e.g., 15.34+0.43−0.23×10²³ m)
  • Value(uncertainty in the last digits)/×/10ⁿ/unit symbol (e.g., 1.604(48)×10⁻⁴ J)
  • Value/±/relative uncertainty(percent)/unit symbol (e.g., 12.34 ± 5% m²)
• {{val}} is meant to be used to automatically handle all of this, but currently has known bugs, principal among them, not displaying some values as typed in the code (see Talk:val). Use with great consideration and always check that it will give the correct results before using it.

Units of measurement

The use of units of measurement is based on the following principles:

• Unambiguousness: Aim to write so you cannot be misunderstood.
• Familiarity: The less one has to look up definitions, the easier it is to be understood.
• International scope: Wikipedia is not country-specific; unless tackling region-specific topics, use international units.

If you have trouble balancing these three bullets, head to the talk pages to consult other editors and try to reach consensus. Mentioning the issue on the MOSNUM talk page and on the article's associated Wikiproject might also be a good idea, especially if the problem is not restricted to a specific article.

Which units to use

• Broadly accepted units should be given preference. Usually, but not always, this means units approved by the Bureau International des Poids et Mesures (BIPM) (SI units, SI derived units, and non-SI units accepted for use with SI) are preferred over other units (e.g., write 25 °C (77 °F) and not 77 °F (25 °C)).

• Since some disciplines use units not approved by the BIPM, or may format them in a way that differs from BIPM-prescribed format, when such units are used by a clear majority of the sources relevant to those disciplines, articles should follow this (e.g., using cc in automotive articles and not cm³). Such use of non-standard units are always linked on first use.

• Familiar units are preferred over obscure units—do not write over the heads of the readership (e.g., a general interest topic such as black holes would best be served by having mass expressed in solar masses, but it might be appropriate to use Planck units in an article on the mathematics of black hole evaporation).
• Uses of units should be consistent within an article. An article should only have one set of primary units (e.g., write A 10 kg (22 lb) bag of potatoes and a 5 kg (11 lb) bag of carrots, not A 10 kg (22 lb) bag of potatoes and an 11 lb (5 kg) bag of carrots).
• In general, the primary units are SI (37 kilometres (23 mi)); however, US customary units are the primary units in US-related topics, and it is permissible to have imperial units as primary units in UK-related topics.
• The use of ambiguous units is discouraged (e.g., do not write gallon, but rather imperial gallon or US gallon). Only in the rarest of instances should ambiguous units be used, often in direct quotations to preserve accuracy to the quoted material.

Unit conversions

• Conversions to and from metric units and US or imperial units should generally be provided. There are some exceptions:

• Articles on scientific topics where there is consensus among the contributors not to convert the metric units, in which case the first occurrence of each unit should be linked.
• When inserting a conversion would make a common expression awkward (the four-minute mile).
• In topics such as the history of maritime law in which imperial units (e.g. miles and nautical miles) are part of the subject, it can be excessive to provide SI conversions at each instance a unit occurs. In such cases, it is best to explicitly mention that this topic will use these units without providing conversion at each instance in the lead or in the introduction, in which case the first occurrence of each unit should be linked.

• Converted values should use a level of precision similar to that of the source value (e.g. write the Moon is approximately 380,000 kilometres (240,000 mi) from Earth, not the moon is approximately 380,000 kilometres (236,121 mi) from Earth).
• In the main text, spell out the main units and use unit symbols or abbreviations for conversions in parentheses (e.g a pipe 5 centimetres (2 in) in diameter and 37 kilometres (23 mi) long).

• When there is consensus to do so, the main units may also be abbreviated in the main text after the first occurrence.

• In a direct quotation, always keep the source units.

• Conversions required for units cited within direct quotations should appear within square brackets in the quote.
• Alternatively, you can annotate an obscure use of units (e.g. five million board feet of lumber) with a footnote that provides conversion in standard modern units, rather than changing the text of the quotation. See the style guide for citation, footnoting and citing sources.

• {{Convert}} or unit-specific templates from Category:Conversion templates can be used to convert and format many common units in accordance with this manual of style.

Unit symbols

Conventions

• In the main body text, the first instances of units of measurements should be spelled out at least once, and perhaps several times for less familiar units before unit symbols are employed. For instance, one should write “…the typical batch is 250 kilograms…” before one later writes “…and then 15 kg of emulsifier is added.” For less common units of measure, editors should not employ unit symbols without first showing the unit symbol parenthetically after the first use of the full unit name; e.g., “The light intensity over the metrology table was 800 lux (lx).”
• Values and unit symbols are separated by a non-breaking space (&nbsp;) (e.g., write 10 m or 29 kg, not 10m or 29kg).

• Exceptions: Non-alphabetic symbols for degrees, minutes and seconds for angles and coordinates are unspaced (e.g., write 5° 24′ 21.12″ N for coordinates, 90° for an angle, but 18 °C for a temperature). See also Manual of Style—Geographical Coordinates.

• Unit symbols are written in upright roman type, never in italics as they could be mistaken for dimensions, constants, or variables (e.g., write "10 m" or "29 kg", not "10 m" or "29 kg).
• Standard symbols for units are undotted (e.g., write m for metre (not m.), kg for kilogram (not kg.), in for inch (not in., " (double quote), or ′′ (double prime)), and ft for foot (not ft., ' (single quote), or ′ (prime))).

• Non-standard abbreviations should be dotted.

• Symbols have no plural form—an s is never appended (e.g., write kg, km, in, lb, not kgs, kms, ins, lbs. Write bit, not bits unless bits used as a word rather than a symbol).
• Units named after persons are not capitalized when written in full (write A pascal is a unit of pressure, not A Pascal is a unit of pressure). This does not apply to "degree Celsius" and "degree Fahrenheit".
• When unit names are combined by multiplication, separate them with a hyphen. A kilogram-calorie (kg·cal) is not the same thing as a kilogram calorie (kcal). Pluralization is achieved by adding an s at the end (e.g., write A force of ten newton-metres).
• When units names are combined by division, separate them with per (e.g., write meter per second, not meter/second). Pluralization is achieved by adding an s to the unit preceding the per since it reads this many units of this per one unit of this (e.g., write An energy flow of over ten joules per second).
• When units are combined by multiplication, use a middle dot (&middot;) to separate the symbols. For example ms is the symbol for a millisecond, while m·s is a metre-second.
• When units are combined by division, use a slash to separate the symbols (e.g., for metre per second use the symbols m/s (not mps)) or use negative exponents (m·s⁻¹).

• There should be no more than one slash per compound unit symbol, e.g., kg/(m·s), not kg/m/s or kg/m·s.

• Powers of unit symbols are expressed with a superscript exponent (write 5 km², not 5 km^2).

• A superscript exponent indicates that the unit is raised to a power, not the unit and the quantity (3 metres squared is 9 square metres, or 9 m²).
• For areas and volumes, squared and cubed US customary or imperial length units may instead be rendered with sq and cu between the number and the unit symbol (write 15 sq mi and 3 cu ft, not 15 mi sq and 3 ft cu).
• The symbols sq and cu are not used with BIPM-approved metric/SI unit symbols.
• Avoid the unicode characters ² and ³. They are harder to read on small displays, and are not aligned with superscript characters (see x¹x²x³x⁴ vs. x¹x²x³x⁴). Instead, use superscript markup, created with .

• Numerical range of values are formatted as (lower value/en dash/higher value/non breaking space/unit symbol) (e.g., write 5.9–6.3 kg, not 5.9 kg – 6.3 kg or 5.9 – 6.3 kg), or can be specified in written form using either unit symbol or unit names, and units can be mention either after both numerical values or after the last (e.g., write from 5.9 to 6.3 kilograms, from 5.9 kilograms to 6.3 kilograms, from 5.9 to 6.3 kg and from 5.9 kg to 6.3 kg are all acceptable, but only one of these format should be in use in a given article).
• When dimensions are given, values each number should be followed by a unit (e.g., write 1 m × 3 m × 6 m, not 1 × 3 × 6 m³ or 1 × 3 × 6 m).

Units and symbols often written incorrectly

• The degree symbol is °. Using any other symbol (e.g., masculine ordinal º or ring above ˚) for this purpose is incorrect.
• The symbol for the bit is bit, not b. The byte may be represented by either one of the symbols B and byte, but not b or o (French octet). Unless explicitly stated otherwise, one byte is eight bits (see History of byte).

• By extension, the symbols for the units of data rate kilobit per second, megabit per second and so on are kbit/s (not kbps or Kbps), Mbit/s (not Mbps or mbps), etc. Similarly, kilobyte per second and megabyte per second are kB/s (not kBps or KBps) and MB/s (not Mbps or MBps).

• The symbol for Celsius degrees, Fahrenheit degrees and kelvins are °C (not C), °F (not F), and K (not °K).
• For reasons of legibility, the preferred symbol for the unprefixed liter is upper-case L.
• If you need to express years as a unit, use the symbol a (from the Latin annum) along with SI prefixes (e.g., write The half life of thorium-230 is 77 ka and The Cambrian is a geologic period that dates from 540 Ma to 490 Ma).

• There are many types of years (see year). When years are not used in the layman's meaning (e.g., Julie is 20 years old) clarify which type of year is meant.

• Roman prefixes are not used (M (10³), MM (10⁶), B (10⁹)). Use SI prefixes instead.

Disambiguation

• Identify and define ambiguous units on their first use in an article.

• Avoid the use of unit abbreviations that have conflicting meanings in common units systems such as SI and US customary units:

• Use nmi (or NM) to abbreviate nautical mile rather than nm (nanometre).
• Use kn to abbreviate knot rather than kt (could be confused with kilotonne) or KN (could be confused with kilonewton).
• Link such units to their definitions on first use.

• Some different units share the same name. These examples show the need to be specific.

• Use nautical mile or statute mile rather than mile in nautical and aeronautical contexts.
• Use long ton or short ton rather than just ton; these units have no symbol or abbreviation and are always spelled out. The metric unit equal to 1000 kilograms is the tonne and is officially known as the metric ton in the US. Whichever name for the metric unit is used, the symbol is "t".
• Use troy or avoirdupois ounce rather than just ounce in articles concerning precious metals, black powder, and gemstones.
• Use fluid ounce explicitly to avoid confusion with weight, and specify, if appropriate, Imperial, US or other.
• Use US or imperial gallon rather than just gallon (and the same logic applies for quarts, pints, and fluid ounces).
• A calorie (symbol cal) refers to a gram calorie while the kilocalorie (symbol kcal) refers to the kilogram calorie (also known as small calorie and large calorie respectively). When used in a nutrition related article, use kilogram unit as the primary unit. For articles with a largely American readership, use dietary calorie(s) with a one-time link to kilogram calorie.

• For bits and bytes, specify whether the binary or decimal meaning of the prefixes kilo (k, K), mega (M), giga (G) and tera (T) is intended. See Quantities of bytes and bits.

• In tables and infoboxes, use unit symbols and abbreviations—do not spell them out.
• It may be appropriate to note that given quantities and conversions are approximate.

• When part of a full sentence, write approximately in full (e.g., write Earth's radius is approximately 6,400 kilometres, not Earth's radius is approx. 6,400 kilometers or Earth's radius is ~ 6,400 kilometers).
• In tables, infoboxes, or within brackets, use a tilde (~) or use approx. (e.g, write The capacity of a ship is sometimes expressed in gross register tons, a unit of volume defined as 100 cubic feet (~2.83 m³)).
• Do not note a conversion as approximate where the initial quantity has already been noted as such, (e.g., write Earth's radius is approximately 6,400 km (4,000 mi), not Earth's radius is approximately 6,400 km (approx. 4,000 mi).

Quantities of bytes and bits

In quantities of bits and bytes, the prefixes kilo (abbreviated k or K), mega (M), giga (G), etc. are ambiguous. They may be based on a decimal system (like the standard SI prefixes), meaning 10³, 10⁶, 10⁹, etc., or they may be based on a binary system, meaning 1024 (2¹⁰), 1024², 1024³, etc. The binary meanings are more commonly used in relation to solid-state memory (such as RAM), while the decimal meanings are more common for data transmission rates and disk storage.

The following recommendations are made for the use of these prefixes in Wikipedia articles:

• Editors should specify if the binary or decimal meanings of K, M, G, etc. are intended as the primary meaning. Consistency within each article is desirable, but the need for consistency may be balanced with other considerations.

• The definition most relevant to the article should be chosen as primary one for that article (e.g., specify a binary definition in an article on RAM, decimal definition in an article on hard drives, and a binary definition for Windows file sizes, despite files usually being stored on hard drives).
• Where consistency is not possible, specify wherever there is a deviation from the primary definition.

• Disambiguation should be shown in bytes or bits, with clear indication of whether in binary or decimal base. There is no preference in the way to indicate the number of bytes and bits, but the notation style should be consistent within an article. Acceptable examples include:

A 64 MB (64 × 1024² bytes) video card and a 100 GB (100 × 1000³ bytes) hard drive

A 64 MB (64 × 2²⁰ bytes) video card and a 100 GB (100×10⁹ bytes) hard drive

A 64 MB (67,108,864 bytes) video card and a 100 GB (100,000,000,000 bytes) hard drive

Avoid inconsistent combinations such as A 64 MB (67,108,864 bytes) video card and a 100 GB (100 × 1000³ bytes) hard drive. Footnotes, such as those seen in Power Macintosh 5500, may be used for disambiguation.

The IEC standard prefixes kibi-, mebi-, gibi-, etc. (symbols Ki, Mi, Gi, etc.) are not familiar to most Wikipedia readers, so are not to be used except under the following circumstances:

• when the article is on a topic where the majority of cited sources use the IEC prefixes,
• when directly quoting a source that uses the IEC prefixes,
• in articles specifically about or explicitly discussing the IEC prefixes.

Currencies

See also: WikiProject Numismatics: Article titles

Which one to use

• In country-specific articles, such as Economy of Australia, use the currency of the country.
• In non-country-specific articles such as Wealth, use US dollars (US$123), the dominant reserve currency of the world. Some editors also like to provide euro and/or pound sterling equivalents, formatted as described in the next section.
• If there is no common English abbreviation or symbol, use the ISO 4217 standard.

Formatting

• Fully identify a currency on its first appearance (AU$52); subsequent occurrences are normally given without the country identification or currency article link (just $88), unless this would be unclear. The exception to this is in articles related entirely to US- or UK-related topics, in which the first occurrence may also be shortened and not linked ($34 and £22, respectively), unless this would be unclear. Avoid over-identifying currencies that cannot be ambiguous; e.g., do not place EU or a similar prefix before the € sign.
• Do not place a currency symbol after the figure (123$, 123€, 123£), unless the symbol is normally written thus. Likewise, do not write $US123 or $123 (US).
• Currency abbreviations that come before the number are unspaced if they consist of or end in a symbol (£123, €123), and spaced if alphabetic (R 75).
• Ranges are preferably formatted with one rather than two currency identifiers ($250–300, not $250–$300).
• Conversions of less familiar currencies may be provided in terms of more familiar currencies, such as the US dollar, euro or pound sterling. Conversions should be in parentheses after the original currency, rounding to the nearest whole unit, with at least the year given as a rough point of conversion rate reference; for example, 1,000 Swiss francs (US$763 in 2005).
• For obsolete currencies, provide if possible an equivalent, formatted as a conversion, in the modern replacement currency (e.g. decimal pounds for historical pre-decimal pounds-and-shillings figures), or at least a US-dollar equivalent as a default in cases where there is no modern equivalent.
• When possible, always link the first occurrence of a symbol for lesser-known currencies (₮146); some editors consider it unnecessary to link the symbols of well-known currencies, but doing so can often be helpful to readers, as many countries use "dollars" or "pounds" as their base currency, and not all readers are familiar with the euro.
• The pound sterling is represented by the £ symbol, with one horizontal bar. The double-barred ₤ symbol is ambiguous, as it has been used for Italian lire and other currencies as well as that of the British. For non-British currencies that use pounds or a pound symbol (e.g. the Irish pound, IR£) use the symbol conventionally preferred for that currency.

Common mathematical symbols

See also: Manual of Style (mathematics).

• For a negative sign or subtraction operator, use a minus sign (−). You can input a minus sign by either keying in &minus; or by clicking on it in the insert box beneath the edit window (located between the ± and × signs). Do not use an en dash (–), do not use a hyphen (-) unless writing code, and do not use an em dash (—).
• For a multiplication sign, use ×, which is input by clicking on it in the edit toolbox under the edit window or by keying in &times; (however, the letter x is accepted as a substitute for "by" in such terms as "4x4").

Unnecessary vagueness

Use accurate measurements whenever possible.

Geographical coordinates

For draft guidance on, and examples of, coordinates for linear features, see Wikipedia:WikiProject Geographical coordinates/Linear.

Quick guide:

Geographical coordinates on Earth should be entered using a template to standardize the format and to provide a link to maps of the coordinates. As long as the templates are adhered to, a robot performs the functions automatically.

First, obtain the coordinates. Please don't be overly precise.

Two types of template are available:

• {{coord}}, which has replaced the coor family (and combined their functionality), offers users a choice of display format through user styles, emits a Geo microformat, and is supported by Google Earth.
• Infoboxes such as {{Infobox settlement}}

Depending on the form of the coordinates, the following formats are available.

For just degrees (including decimal values):

{{coord|dd|N/S|dd|E/W}}

For degrees/minutes:

{{coord|dd|mm|N/S|dd|mm|E/W}}

For degrees/minutes/seconds:

{{coord|dd|mm|ss|N/S|dd|mm|ss|E/W}}

where:

• DD, MM, SS are the degrees, minutes, seconds, listed in sequence
• N/S is either N or S, depending on which hemisphere, and
• E/W is either E or W, depending on which hemisphere
• negative values may be used in lieu of S and E

For example:

The city of Oslo, located at 59° 55′ N, 10° 44′ E, enter:

{{coord|59|55|N|10|44|E}} — which becomes 59°55′N 10°44′E / 59.917, 10.733

A country, like Botswana, less precision is appropriate:

{{coord|22|S|24|E}} — which becomes 22°S 24°E / -22, 24

Higher levels of precision are obtained by using seconds

{{coord|33|56|24|N|118|24|00|W}} — which becomes 33°56′24″N 118°24′00″W / 33.94, -118.4

Coordinates can be entered as decimal values

{{coord|33.94|S|118.40|W}} — which becomes 33°56′S 118°24′W / -33.94, -118.4

Increasing or decreasing the number of decimal places can control the precision. Trailing zeroes should be included.