Wikipedia:Manual of Style/Dates and numbers: Difference between revisions

This guideline is a part of the English Wikipedia's Manual of Style. It is a generally accepted standard that editors should attempt to follow, though occasional exceptions may apply. Any substantive edit to this page should reflect consensus. When in doubt, discuss first on the talk page.

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

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 ruled that when either of two styles is acceptable, it is inappropriate for an editor to change an article from one style to another unless there is a substantial reason to do so. Edit warring over optional styles 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.

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

• In compound items in which numerical and non-numerical elements are separated by a space, a non-breaking space (or hard space) is recommended to avoid the displacement of those elements at the end of a line.

A hard space can be produced with the HTML code   instead of the space bar: 19 kg yields a non-breaking 19 kg. 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 sentence.

Template {{nowrap}} has some inadequacies: 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 still 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.

Avoid statements that will date quickly, except on pages that are regularly updated, such as those that cover current events. Avoid such items as recently and soon (unless their meaning is clear in a storyline), currently (except on rare occasions when it is not redundant), and is soon to be superseded. Instead, use either:

• more precise items (since the start of 2005; during the 1990s; is expected to be superseded by 2008); or
• an as of phrase (as of August 2007), which is a signal to readers of the time-dependence of the statement, and to later editors of the need to update the statement (see As of).

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.

• Wikipedia does not use ordinal suffixes or articles, or put a comma between month and year in partial dates.

Incorrect	February 14th, 14th February, the 14th of February
Correct	14 February, February 14
Incorrect	October, 1976
Correct	October 1976

• Date ranges are preferably given with minimal repetition (5–7 January 1979; September 21–29, 2002), using an unspaced en dash. If the autoformatting function is used, the opening and closing dates of the range must be given in full (see Autoformatting and linking) and be separated by a spaced en dash.
• Rarely, 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); this cannot be done using the autoformatting function.
• 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".
• ISO 8601 dates (1976-05-31) are uncommon in English prose, and are generally not used in Wikipedia. However, they may be useful in long lists and tables for conciseness and ease of comparison.

In general, the following formats are acceptable:

• International format: 14 February and 14 February 1990 (common in many countries);
• American format: February 14 and February 14, 1990 (more common in the US).

Disputes between editors over date formats are avoided by using three simple guidelines. See also autoformatting and linking.

Consistency within articles

The same format should be used in the main text, footnotes and references of each article, except for:

• dates within quotations and titles, where the original format is retained;
• explicit comparisons of date formatting.

Strong national ties to a topic

Articles on topics with strong ties to a particular English-speaking nation should generally use the more common date format for that nation; articles related to Canada may use either format consistently. Articles related to other countries that commonly use one of the two acceptable guidelines above should use that format.

Retaining the existing format

If an article has evolved using predominantly one format, the whole article should conform to that variety, unless there are reasons for changing it on the basis of strong national ties to the topic.

In the early stages of writing an article, the format chosen by the first major contributor to the article should be used, unless there is reason to change it on the basis of 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.

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

• Locations of birth and death are given subsequently rather than being entangled with the dates.
• When only the years are known: "Socrates (470–399 BC) was ..."
• For a person still living: "Serena Williams (born September 26 1981) ...", not "... (September 26 1981–) ..."
• When the date of birth is unknown: "Offa (died 26 July 796) ..."
• When the date of birth is known only approximately: "Genghis Khan (c. 1162 – August 18, 1227) ..."
• When the dates of both birth and death are known only approximately: "Dionysius Exiguus (c. 470 – c. 540) ..."
• When the date of death is unknown, but the person is certainly now dead: "Robert Menli Lyon (born 1789, date of death unknown) ..."
• When only the dates of the person's reign are known, and only approximately: "Rameses III (reigned c. 1180 BCE – c. 1150 BCE) ..."
• When the person 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. 760–72) ..."
• When the person is known to have been alive as early as about 660, and to have died in 685: "Aethelwalh (fl. c. 660–85) ..."

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.

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.

• Months are expressed as whole words (February, not 2), except in the ISO 8601 format. 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).

• 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.
• Years

• Years are normally expressed in digits; a comma is not used in four-digit years (1988, not 1,988).
• 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 (do not use 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 indicate to the reader an uncertainty on the part of Wikipedia editors rather than on the part of reliable historians.

• 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).
• Centuries and millennia
  • There was no year 0. So 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.
  • Because expressions like the 1700s are ambiguous (referring to a century or a decade), they are best avoided.
• Eras and other very long periods

• 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 1950-01-01", 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.)

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 1582-10-15 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 1752-09-14, and Russia from 1918-02-14 (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 is 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).

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 United States, 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.

• A combination of a day number and a month can be autoformatted by adding square brackets ([[5 November]]). If a year is also given, with a separate link, all three items are autoformatted as a single date. The square brackets instruct the MediaWiki software to format the item according to the date preferences if a setting has been chosen by registered users. The autoformatting mechanism does not work for

• registered users that have not made a setting
• unregistered users.

Links to date elements that do not contain both a day number and a month are not required; for example, solitary months, solitary days of the week, solitary years, decades, centuries, and month and year combinations. Such links must not be used unless the reader needs to follow the link to understand the topic; see WP:CONTEXT. Autoformatting must not be used for the following purposes:

• piped links to date elements ([[20 June|20]], [[20 June]] [[1997 in South African sport|1997]]) (several forms of piped links break the date formatting function);
• links to date ranges in the same calendar month e.g. December 13–17 or the night of 30/31 May – the autoformatting mechanism will damage such dates (30/May 31);
• links to date elements on disambiguation pages;
• links to date elements in article and section headings; and
• links to date elements in quotations (unless the original text was wikilinked).

The following table shows how the autoformatting mechanism behaves. The preference settings that a logged-in, registered user has chosen are displayed in the second row.

What you type	What logged-in registered users see (settings on first row)					What others will see*	Note
--	January 15, 2001	15 January 2001	2001 January 15	2001-01-15	No preference	--	--
[[May 15]]	May 15	15 May	May 15	May 15	May 15	May 15
[[15 May]]	May 15	15 May	May 15	May 15	May 15	15 May
[[May 15]], [[2005]]	May 15, 2005	15 May 2005	2005 May 15	2005-05-15	May 15, 2005	May 15, 2005
[[May 15]] [[2005]]	May 15, 2005	15 May 2005	2005 May 15	2005-05-15	May 15, 2005	May 15, 2005	**
[[15 May]] [[2005]]	May 15, 2005	15 May 2005	2005 May 15	2005-05-15	15 May 2005	15 May 2005
[[15 May]], [[2005]]	May 15, 2005	15 May 2005	2005 May 15	2005-05-15	15 May 2005	15 May 2005	**
[[2005-05-15]]	May 15, 2005	15 May 2005	2005 May 15	2005-05-15	2005-05-15	2005-05-15
[[2005 May 15]]	2005 May 15	2005 May 15	2005 May 15	2005 May 15	2005 May 15	2005 May 15
[[15 May 2005]]	15 May 2005	15 May 2005	15 May 2005	15 May 2005	15 May 2005	15 May 2005
[[May 15, 2005]]	May 15, 2005	May 15, 2005	May 15, 2005	May 15, 2005	May 15, 2005	May 15, 2005
[[15-05-2005]]	15-05-2005	15-05-2005	15-05-2005	15-05-2005	15-05-2005	15-05-2005
[[05-15-2005]]	05-15-2005	05-15-2005	05-15-2005	05-15-2005	05-15-2005	05-15-2005
indicates a code that produces no autoformatting and is thus likely to display as a dead link * Non-registered users and registered users not logged in ** Displays a date format that differs from wikitext, even for users without a preference

The following section's wording or inclusion in this policy or guideline is disputed or under discussion. Please see the relevant talk page discussion for further information.

In the body of an article, single-digit whole numbers (from zero to nine) are given as words; numbers of more than one digit are generally rendered as figures, and alternatively as words if they are expressed in one or two words (sixteen, eighty-four, two hundred, but 3.75, 544, 21 million).

• Numbers in mathematical formulas are never spelled out (3 < π < 22/7, not three < π < 22 sevenths).
• 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.). Spell them out in historical references, such as Seventh of March speech and Fifth of November.
• Figures normally do not begin or end a sentence; they can be confused with a number following an abbreviation (the last word of the preceeding sentence) or a number with decimal point, respectively. Spelling out the number, or recasting the sentence, can often avoid the problem.
• In tables and infoboxes, all numbers are expressed as numerals when offered as data. Numbers within a table's expounding text and comments should be consistent with the general rule.
• Within a context or a list, style should be consistent (either 5 cats and 32 dogs or five cats and thirty-two dogs, not five cats and 32 dogs).
• For instances where numerals may cause confusion, use words instead (thirty-six 6.4-inch rifled guns, not 36 6.4-inch rifled guns).
• Fractions are normally spelled out; use the fraction form if they occur in a percentage or with an abbreviated unit (⅛ mm, but never an eighth of a mm) or they are mixed with whole numerals.
• Decimal representations containing a decimal point are not spelled out (1.00, 3.14159).
• A small whole number in a percentage may be spelled out, but only if the percent sign is not used (three percent or 3%, not three %). If in a context some percentages are presented with numerals, then all are to be presented that way.
• Ordinal numbers are spelled out using the same rules as for cardinal numbers. The exception is ordinals for centuries, which may be expressed in digits (the 5th century CE; 19th-century painting). The ordinal suffix (e.g., th) is not superscripted (23rd and 496th, not 23^rd and 496^th). Spell out ordinal numbers when they are inclusive used as the first word of a proper name (e.g. Fourth Amendment; Seventeenth Judicial District). Do not spell out ordinal numbers in the proper names of military units.
• Proper names and formal numerical designations 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.
• The numeral and the spelled-out number can have different meanings, as in these two phrases:
  • Every number except one, in which one refers to the number of exceptions (for example, the one exception could be the number 42), although rephrasing to avoid the ambiguity would be better; and
  • Every number except 1, in which the specific number 1 is the exception (this usage is not ambiguous).

• 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).

• Commas are used to break the sequence every three places left of the decimal point; spaces or dots are never used in this role (2,900,000, not 2 900 000).
• Large rounded 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 is probably appropriate, but 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.
• 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.

• 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 minus one and plus 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.

• 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.

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.

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.

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).

• In general, the main units are metric; for example, 37 kilometres (23 mi), but
  • for US-related articles, and where idiom prefers it, the main units are US units; for example, 23 miles (37 km).
  • for UK-related articles, the main units may be imperial (consistently within an article).
• In scientific articles, use the units employed in the current scientific literature on that topic. This will usually be SI, but not always; for example, natural units are often used in relativistic and quantum physics, and Hubble's constant should be quoted in its most common unit of (km/s)/Mpc rather than its SI unit of s⁻¹.
• If editors cannot agree on the sequence of units, put the source value first and the converted value second. If the choice of units is arbitrary, use SI units as the main unit, with converted units in parentheses.
• American English spells metric units with final -er (kilometer); in all other varieties of English, including Canadian English, -re is used (kilometre).

Use terminology and symbols commonly employed in the current literature for that subject and level of technicality. When in doubt, use the units of measure, prefixes, unit symbols, number notation, and methods of disambiguation most often employed in reliable periodicals directed to a similar readership.

Wikipedia’s mission is to communicate with minimal confusion so that readers can learn about a subject and are primed as well as possible to learn even more in their studies elsewhere. There are three important elements in determining what terminology and units of measure are best suited for a given article:

Preference for modern units

Wikipedia generally prefers modern systems of measurement, such as the SI, over U.S. customary units or the imperial system. Unless there is a good reason to do otherwise, write “the auto weighs 1450 kg (3200 lb)”, not the reverse.

Discipline-specific practices

Wherever a discipline consistently uses its own units—either conventional or metric rather than SI—Wikipedia should mirror those practices so readers will be conversant and knowledgeable in the discipline. Editors should write…

• “a 450 cc Honda motorcycle engine” and never “a 450 ml” or “450 cm³ Honda motorcycle engine”;
• “Saudi Arabia exported 9.0 million barrels of crude”, but not “Saudi Arabia exported 1.43 million cubic meters of crude” (unless an article is about Canadian oil production or you are quoting a source that observes Canadian practices);
• “a gravity gradient of 3.1 µGal/cm”, not “a gravity gradient of 3.1×10⁻⁶ s^–2”, in the science of gravimetry.

Parenthetical conversions should be given where appropriate and should generally also follow the practices in current literature on that subject unless there is good reason to do otherwise. Often the conversions will be to modern systems. Even within the narrow discipline of piston engines in ground transportation, there is a range of permissible ways to show conversions; there is often no best way. For instance, writing "a 450 cc (450 cm³) motorcycle engine" is inappropriate even though it is in conformance with the SI. "The Ford 351 Cleveland engine had an actual displacement of 351.9 cubic inches (5,766 cc)” is appropriate for a historical, American-made engine. "The Dodge 5.7 L Hemi has a displacement of 5,654 cc (345.0 in³)" is appropriate for a modern, American-label engine that is classified in liters. But writing "the Ferrari Dino V12 engine has a displacement of 334.0 cubic inches" would be inappropriate in an article primarily about a European-made sports car.

There have been occasions where standards bodies have proposed new units of measure to better adhere to the SI and/or to address ambiguities but the new units didn’t see widespread adoption. Because existing prefixed forms of the byte are ambiguous ("KB", for instance, can mean either 1024 or 1000 bytes depending on context), the IEC in 1999 released its IEC 60027-2 amendment, introducing new prefixes for bytes and bits, such as "kibibyte (KiB)", "kibibit (Kibit)", and "mebibyte (MiB)". However, the IEC prefixes have seen little real-world adoption and are therefore unfamiliar to the typical Wikipedia reader. In keeping with the principle of follow current literature, editors should use the conventional binary prefixes, such as "kilobyte (KB)" and "megabyte (MB)", for general-interest articles and clarify their meaning where necessary using familiar techniques (subject to "Binary prefixes", below).

Level of difficulty (Do not write over the heads of the readership)

For some topics, there are multiple modern systems of measurement to choose from but some would generally be unsuitable for use in articles directed to a general-interest readership. For instance, the Planck units would typically be suitable only for advanced articles directed to expert readers—for example, an article on the mathematics of black hole evaporation—whereas an article on black holes directed to a general-interest readership should describe their mass in terms of solar mass. Level of difficulty also applies to the decision as to whether or not scientific notation should be employed and at what point it should be begin (for values as low as one million?). Here again, editors should look towards current literature on that subject for guidance in selecting level-appropriate units of measure, unit symbols, number notation, and terminology.

• Conversions to and from metric and US units are generally provided. There are exceptions, including:
  • 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;
  • where 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 (for example, miles and nautical miles) are part of the subject, it is useful to provide metric conversions, but excessive to convert exactly the same unit and value every time it occurs.
• In the main text, spell out the main units and use unit symbols or abbreviations for conversions in parentheses; for example, a pipe 100 millimetres (4 in) in diameter and 16 kilometres (10 mi) long or a pipe 4 inches (100 mm) in diameter and 10 miles (16 km) long. The exception is that where there is consensus to do so, the main units may also be abbreviated in the main text after the first occurrence.
• Converted values should use a level of precision similar to that of the source value; for example, the Moon is 380,000 kilometres (240,000 mi) from Earth, not ... (236,121 mi).
• {{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.
• In a direct quotation:
  • conversions required for units cited within direct quotations should appear within square brackets in the quote;
  • if the text contains an obscure use of units (e.g., five million board feet of lumber), annotate it with a footnote that provides standard modern units, rather than changing the text of the quotation.
• Measurements should be accompanied by a proper citation of the source using a method described at the style guide for citation.
• Where footnoting or citing sources for values and units, identify both the source and the original units.
• Editors are encouraged to identify and define ambiguous units on their first use in an article. Examples of units in common use that need disambiguation are gallon (US or imperial), megabyte (1000², 1024² or 1000×1024 B), mile (international or nautical) and ton (long, short or metric). A more complete list of ambiguous units is provided under the heading Unit symbols and abbreviations below.

• In accordance with the rules of CGPM, NIST, National Physical Laboratory (UK), unit symbols are in upright, roman type.
• Standard symbols for units are undotted. For example, ‘m’ for metre and ‘kg’ for kilogram (not ‘m.’ or ‘kg.’), ‘in’ for inch (not ‘in.’, ‘"’ or ‘″’), ‘ft’ for foot (not ‘ft.’, ‘'’ or ‘′’) and ‘lb’ for pound (not ‘lb.’ or ‘#’).
• Symbols have no plural form, i.e. an s is never appended (‘kg’, ‘km’, ‘in’, ‘lb’, ‘bit’, not ‘kgs’, ‘kms’, ‘ins’, ‘lbs’, ‘bits’).
• When unit names are combined by multiplication, separate them with a space or hyphen (newton metre or newton-metre).
• When units are combined by multiplication, use a middle dot to separate the symbols (e.g., for newton metre, use ‘N·m’, not ‘N m’, ‘Nm’, ‘N-m’ or ‘N•m’).
• When units are combined by division, use a slash to separate the symbols (e.g., for metre per second, use the symbol ‘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’).
• 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. Decimal or binary prefix symbols may be added to either unit symbol. The choice of decimal or binary should be made with regard to common usage in the subject area, and clarification is recommended.
• Temperatures are always accompanied by ‘°C’ for degrees Celsius, ‘°F’ for degrees Fahrenheit, or ‘K’ for kelvins (“35 °C”, “5,000 K”); these three symbols are always upper-case. For the first two, the unit is a degree; for the last, it is kelvin rather than degree Kelvin (i.e. do not use “5,000 °K”)
• Values and unit symbols are spaced (“25 kg”, not “25kg”). The exceptions are the non-alphabetic symbols for degrees, minutes and seconds for angles (the coordinate is 5° 24′ 21.12″ N, the pathways are at a 90° angle, but the average temperature is 18 °C).
• Powers of unit symbols may always be expressed with a superscript exponent (“5 km²”). 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 U.S. customary length units may instead be rendered with ‘sq’, and cubic with ‘cu’, between the number and the unit symbol (“15 sq mi”, “3 cu ft”, not “3 ft cu”).
  • The symbols ‘sq’ and ‘cu’ may never be used with metric unit symbols.
• In tables and infoboxes, use unit symbols and abbreviations; do not spell them out.
• 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’ (kilotonne) or ‘kts’.
  • 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 (the metric unit—the tonne—is also known as the metric ton).
  • 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, U.S. or other.
  • Use US or imperial gallon rather than just gallon (and the same logic applies for quarts, pints, and fluid ounces).
  • Use small calorie or large calorie (also known as gram calorie or kilogram calorie) rather than just 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 also the next section.
• Ranges are preferably formatted with one rather than two unit signifiers (5.9–6.3 kg, not 5.9 kg – 6.3 kg).
• In spatial values each number should be followed by a unit, e.g. “1 m × 3 m × 6 m”, not “1 × 3 × 6 m³” or “1 × 3 × 6 m”.

The following section's wording or inclusion in this policy or guideline is disputed or under discussion. Please see the relevant talk page discussion for further information.

In most measurement systems the symbols k^[1], M, and G (representing prefixes kilo-, mega-, and giga-, respectively) follow the SI prefixe convention using powers of 1000 (10³), that is, k (kilo) = 1,000, M (mega) = 1,000,000 and G (giga) = 1,000,000,000, etc.

However, when measuring bits and bytes, there are two different de facto standards for defining the symbols K, M, and G, one following the SI prefixes convention using powers of 1000 (10³) and one in powers of 1024 (2¹⁰). To resolve this ambiguity, the IEC in 1999 introduced new binary prefixes including kibi-, mebi-, gibi-, and symbols such as Ki, Mi, Gi to specify binary multiples of a quantity. These replacements for the historical units have gained only limited acceptance outside the standards organizations. Most publications, computer manufacturers and software companies continue to use the historical units (KB, MB, GB) with either meaning; sometimes both meanings appear in the same line of an article or advertisement^[2].

There is no consensus to use the newer IEC-recommended prefixes in Wikipedia articles to represent binary units. There is consensus that editors should not change prefixes from one style to the other, especially if there is uncertainty as to which term is appropriate within the context—one must be certain whether "100 GB" means binary not decimal units in the material at hand before disambiguation. When this is certain the use of parentheses for binary prefixes, for example "256 KB (256×2¹⁰ bytes)", is acceptable, as is the use of footnotes to disambiguate prefixes. Use of IEC prefixes is also acceptable for disambiguation (256 KiB). When in doubt, stay with established usage in the article, and follow the lead of the first major contributor. Prefixes in directly quoted passages are never changed; if explanation is necessary, use a more exact measurement in square brackets.

Bit and/or byte measures that typically use decimal multiples:

• Capacity of hard disk drives
• Capacity of DVDs
• Computer network and bus speeds

Bit and/or byte measures that typically use binary multiples:

• Capacity of semiconductor storage, e.g. memory and cache sizes
• Capacity of CD-ROMs

Use accurate measurements whenever possible.

Vague	Precise
The wallaby is small	The average male wallaby is 1.6 metres (63 in) from head to tail.
Prochlorococcus marinus is a tiny cyanobacterium.	The cyanobacterium Prochlorococcus marinus is 0.5 to 0.8 micrometre across.
The large oil spill stretched a long way down the Alaskan coast.	The oil spill that drifted down the Alaskan coast was 3 statute miles (5 km) long and 1,000 feet (300 m) wide.

See orders of magnitude and the talk page there for ongoing, possibly resolved debate on which style of exponent notation to use for large numbers.

See also: WikiProject Numismatics: Article titles

• 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). Some editors also like to provide euro and/or UK pound sterling equivalents, formatted as described in the next section.
• If there is no common English abbreviation or symbol, use the ISO 4217 standard.

• 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 the US and the UK, in which the first occurrence may also be shortened and not linked ($34 and £22, respectively), unless this would be unclear. Avoid over-identifying currencies that cannot be ambiguous; e.g. do not place EU or a similar prefix before the € sign.
• Do not place a currency symbol after the value (123$, 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 signifiers ($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 UK pound. 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. UK 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 UK 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 the British one. For non-UK currencies that use pounds or a pound symbol (e.g. the Irish punt, IR£) use the symbol conventionally preferred for that currency.

See also: Manual of Style (mathematics).

• For a negative sign or subtraction operator, use a minus sign (−), input by clicking on it in the insert box beneath the edit window or by keying in &minus;, or an en dash (see En dashes); do not use a hyphen, unless writing code, or 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").
• The following signs are spaced on both sides:
  • plus, minus, plus or minus (as operators): + − ±
  • multiplication and division: × ÷
  • equals, does not equal, is approximately equal to: = ≠ ≈
  • is less than, is less than or equal to, is greater than, is greater than or equal to: < ≤ > ≥

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, the functions are performed automatically by a robot. Due to planned enhancements in functionality, this information is subject to change.

Two types of template are available:

• {{coor *}}, which is used in most articles and supported by all re-users, such as Google Earth and Wikipedia-World. This however has been superseded by {{coord}} below.
• {{coord}}, which combines the functionality of the coor family, offers users a choice of display format through user styles, emits a Geo microformat, and is supported by Google Earth.