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Wikipedia:Manual of Style (dates and numbers)

This Manual of Style has the simple purpose of making things look alike - it is a style guide. The following rules don't claim to be the last word. One way is often as good as another, but if everyone does it the same way, the Wikipedia will be easier to read and easier to use, not to mention easier to write and easier to edit.

New contributors are reminded that clear, informative and unbiased writing is always more important than presentation and formatting. Writers are NOT expected or required to follow all or any these rules: the joy of wiki editing is that perfection is not required. Copy-editing wikipedians will be referring to these pages when weeding, and pages will be gradually made to conform with this guide.

Table of contents


A page title that is just a number is always a year. Pages also exist for days of the year, decades, centuries and even millennia. The formats are:

  • 474
    • [[474]]
  • 474 BC (note no periods)
    • [[474 BC]]
  • 18th century (Note century is not capitalized. Note also that "1700s" is not a century, but a decade as illustrated below.)
    • [[18th century]]
  • 10th century BC
    • [[10th century BC]]
  • 1830s (note no apostrophe)
    • [[1830s]]
  • December, 1983 (note that December is not linked)
    • December, [[1983]]
  • 320s BC
    • [[320s BC]]

Articles for the year 500 BC and earlier should be redirected to the relevant decade. Articles for the year 1700 BC and earlier should be redirected to the relevant century. Articles for the year 4000 BC and earlier should be redirected to the relevant millennium.

The use of day/month/year versus month/day/year is currently under discussion. The current Manual of Style recommendation is that all dates (outside quotes) should be in the following format:

However, several wikipedians believe this should be changed in various ways, such as recommending that all dates should be in this format instead:

Pros and cons of the various options are discussed on the talk page. All the dates pages in day/month format have been redirected to date pages in month/day format. For example, 1 January redirects to January 1 and 13 February redirects to February 13.

Bad formats

What not to do:

  • Do not use numbers for expressing a month. Always express a month as a whole word (e.g. "February") to avoid ambiguity.
  • Do not use two digits for expressing a year or decade, as in '80s, unless discussing the years from 10 to 99. An encyclopedia deals with all of history, not just the last hundred years, so always use four digits for years and decades.
  • Do not use piped links to "years in music" or analogous pages (e.g. [[1983 in music|1983]]). See Wikipedia:Wikiproject Music standards.
  • In general, avoid using multiple date formats in the same article.

Quotes do not need to conform to the wikipedia manual of style. In other words, a paragraph like the (fictional) one below is fine:

  • Tony Blair, responding to critics within his party, said "The world has totally changed since the 11th of September". He was echoing earlier sentiments by Ronald McDonald, who said that "nine-eleven was the day that the American public woke up to the reality of terrorism".

Time format and time zones

Times should be written in a 24 hour format (HH:MM:SS). The problem with am/pm notation is that it often makes it less-trivial to convert between different time zones. For example, to convert December 25 at 4:45pm (UTC +1), to another time zone, say UTC -8, one would need either to subtract 4:45 and then 4:15, or translate it to 24 hour format (16:45) and then subtract 9. Another factor is that after-midnight/past-midnight notation is strictly time zone-dependent, and may confuse a person living with a different sunrise/sunset periods.

Another guideline for dealing with different time zones is that when writing a certain date and time, first consider where the event happended 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 some cracker in Japan hacked the Pentagon, use the time zone for the Pentagon.

If you know it, include the UTC date and time of the event in the article, indicating its UTC.

Style for numbers, weights, and measures

Very large numbers, such as pinball scores, should be divided up by commas every three places. In scientific contexts, scientific notation is preferred: see below.

The issue of whether all units should be metric (SI) or Imperial (or American style) is acceptable is being debated at Wikipedia:Measurements Debate. In summary, metric is more widespread and regular, but some Americans don't use it. In addition, the names of American and Imperial measurements are sloppy and don't always denote the same quantities.

In any scientific context, be it physics, chemistry and other, always use SI units. Unless for any historic referrence or other particular reason, it is not necessary to state imperial units in parenthesis.

If using American or Imperial, give metric as a courtesy. If using metric, remember that many readers will not know what you mean and will be aided by the equivalent.

These need not be exact equivalents unless exact measurement is involved. And if the quantity is always given in one form, you need not perform any conversion at all. Here is a good site for online conversions (http://www.onlineconversion.com/) you might find useful.

Use standard abbreviations for metric units, m for meter, kg for kilogram, etc (see SI for the list), and two-letter abbreviations for inch-pound units, in=inch, ft=foot, yd=yard, mi=mile, lb=pound, gal=gallon, pt=pint, qt=quart, and so forth. (bear in mind that gallon & pint are ambiguous units -- they have several values)

Measurements (both number and unit together) of dimensions with existing orders of magnitude pages should be linked to the appropriate page. If no order of magnitude page exists for it, link the unit to its full name.

Velocities should be given in m/s by default, but in km/h when this is conventional (speed limits etc.).

Areas of land areas should be given in km², which is entered as km&sup2;. This form is preferable to km<sup>2</sup>, which adds extra line leading. Smaller areas in m² etc. Volumes in m³, cm³ etc. Note that the compact superscript style works only for 2 and 3. This means that the <sup> style has to be used when general superscripts are required, as in the examples below.


  • The highest score recorded for the Deuces High pinball game was 11,933,750.
  • The hippopotamus stands 1.5 m (5 ft) at the shoulders and weighs between 2700 and 4500 kg (roughly 6000 to 10000 lb).
  • The first sub-four-minute mile was run by Roger Bannister.
  • The 155 mm diameter projectile offers a wide range of options for battlefield usage.
  • 102 = 100
    • 10<SUP>2</SUP> = 100
  • A large number such as 156,234,000,000,000,000,000,000,000,000 can be concisely recorded as 1.56234 × 1029, and a small number such as 0.0000000000234 can be written as 2.34 × 10-11.
    • A large number such as 156,234,000,000,000,000,000,000,000,000 can be concisely recorded as 1.56234 × 10<SUP>29</SUP>, and a small number such as 0.0000000000234 can be written as 2.34 × 10<sup>-11</sup>.

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.

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