# 12-hour clock

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Time counting system

"AM and PM" redirects here. For other uses, see [AM PM (disambiguation)](/source/AM_PM_(disambiguation)).

"Ante meridiem" redirects here. For the meridian 180° both east and west of the prime meridian in a geographical coordinate system, see [Antimeridian](/source/180th_meridian).

The **12-hour clock** is a time convention in which the 24 hours of the day are divided into two periods: **a.m.** (from [Latin](/source/Latin) ***ante meridiem***, translating to "before midday") and **p.m.** (from Latin ***post meridiem***, translating to "after midday").[1][2] Each period consists of 12 hours numbered: 12 (acting as 0),[3] 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11. The 12-hour clock has been developed since the [second millennium BC](/source/Second_millennium_BC) and reached its modern form in the 16th century.

The 12-hour time convention is common in several English-speaking nations and former [British colonies](/source/British_Empire), as well as a few other countries. In English-speaking countries: "12 p.m." usually indicates noon, while "12 a.m." means midnight, but the reverse convention has also been used (see [§ Confusion at noon and midnight](#Confusion_at_noon_and_midnight)).[4][5][6] "Noon" and "midnight" are unambiguous.

Notation according to various authorities 24-hour clock 12-hour clock 00:00 midnight 12:00 p.m.[a] (start of the day) 12:00 a.m.[a] (start of the day) 01:00 1:00 a.m. 02:00 2:00 a.m. 03:00 3:00 a.m. 04:00 4:00 a.m. 05:00 5:00 a.m. 06:00 6:00 a.m. 07:00 7:00 a.m. 08:00 8:00 a.m. 09:00 9:00 a.m. 10:00 10:00 a.m. 11:00 11:00 a.m. 12:00 midday noon 12:00 a.m.[a] (start of the day) 12:00 p.m.[a] 13:00 1:00 p.m. 14:00 2:00 p.m. 15:00 3:00 p.m. 16:00 4:00 p.m. 17:00 5:00 p.m. 18:00 6:00 p.m. 19:00 7:00 p.m. 20:00 8:00 p.m. 21:00 9:00 p.m. 22:00 10:00 p.m. 23:00 11:00 p.m. 24:00 (00:00 of next day) midnight 12:00 p.m.[a] (start of the day) 12:00 a.m.[a] (start of the day) (end of the day) ^ a b c d e f See: 12-hour clock § Confusion at noon and midnight

## History and use

[Exeter Cathedral Astronomical Clock](/source/Exeter_Cathedral_Astronomical_Clock), showing the double-XII numbering scheme

World War II RAF [sector clock](/source/Sector_clock) that can be read either in 12- or 24-hour notation

The natural day-and-night division of a calendar day forms the fundamental basis as to why each day is split into two cycles. Originally there were two cycles: one cycle which could be tracked by the position of the Sun (day), followed by one cycle which could be tracked by the Moon and stars (night). This eventually evolved into the two 12-hour periods which are used today, one called "a.m." starting at midnight and another called "p.m." starting at noon.[1]

The 12-hour clock can be traced back as far as [Mesopotamia](/source/Mesopotamia) and [ancient Egypt](/source/Ancient_Egypt).[7] Both an Egyptian [sundial](/source/Sundial) for daytime use[8] and an Egyptian [water clock](/source/Water_clock) for night-time use were found in the tomb of Pharaoh [Amenhotep I](/source/Amenhotep_I).[9] Dating to c. 1500 BC, these clocks divided their respective times of use into 12 hours each.

The [ancient Romans](/source/Ancient_Rome) also [used a 12-hour clock](/source/Roman_timekeeping): daylight and nighttime were each divided into 12 equal intervals (of varying duration according to the season).[10] The nighttime hours were grouped into four *[watches](/source/Watchkeeping)* (*vigiliae*).[11]

The first mechanical clocks in the 14th century, if they had dials at all, showed all 24 hours using the [24-hour analog dial](/source/24-hour_analog_dial), influenced by astronomers' familiarity with the [astrolabe](/source/Astrolabe) and sundial and by their desire to model the [Earth's apparent motion around the Sun](/source/Earth's_rotation). In [Northern Europe](/source/Northern_Europe) these dials generally used the 12-hour [numbering scheme](/source/Numbering_scheme) in [Roman numerals](/source/Roman_numerals) but showed both *a.m.* and *p.m.* periods in sequence. This is known as the double-XII system and can be seen on many surviving clock faces, such as those at [Wells](/source/Wells_Cathedral_clock) and [Exeter](/source/Exeter_Cathedral#Clock).

Elsewhere in Europe, numbering was more likely to be based on the 24-hour system (I to XXIV). The 12-hour clock was used throughout the [British Empire](/source/British_Empire).

During the 15th and 16th centuries, the 12-hour analog dial and time system gradually became established as standard throughout Northern Europe for general public use. The 24-hour analog dial was reserved for more specialized applications, such as [astronomical clocks](/source/Astronomical_clock) and chronometers.

Most analog clocks and watches today use the 12-hour dial, on which the shorter hour hand rotates once every 12 hours and twice in one day. Some analog clock dials have an inner ring of numbers along with the standard 1-to-12 numbered ring. The number 12 is paired either with a 00 or a 24, while the numbers 1 through 11 are paired with the numbers 13 through 23, respectively. This modification allows the clock to also be read in [24-hour notation](/source/24-hour_notation). This kind of 12-hour clock can be found in countries where the 24-hour clock is preferred.

### Use by country

World map showing the usage of 12 or 24-hour clock in different countries
  24-hour

  24-hour (12-hour orally)

  Both in common use

  12-hour (except in special circumstances such as [aviation](/source/Aviation))

In several countries the 12-hour clock is the dominant written and spoken system of time, predominantly in nations that were part of the former British Empire, for example, the [United Kingdom](/source/United_Kingdom), [Republic of Ireland](/source/Republic_of_Ireland), the [United States](/source/United_States), [Canada](/source/Canada) ([excluding Quebec](/source/Date_and_time_notation_in_Canada#Time_notation_in_French)), [Australia](/source/Australia), [New Zealand](/source/New_Zealand), [South Africa](/source/South_Africa), [India](/source/India), [Pakistan](/source/Pakistan), and [Bangladesh](/source/Bangladesh), and others follow this convention as well, such as [Mexico](/source/Mexico), [Colombia](/source/Colombia), and the former American colony of the [Philippines](/source/Philippines). Even in those countries where the 12-hour clock is predominant, there are frequently contexts (such as science, medicine, the military or transport) in which the 24-hour clock is preferred. In most countries, however, the [24-hour clock](/source/24-hour_clock) is the standard system used, especially in writing. Some nations in Europe and Latin America use a combination of the two, preferring the 12-hour system in colloquial speech but using the 24-hour system in written form and in formal contexts.

The 12-hour clock in speech often uses phrases such as*... in the morning*,*... in the afternoon*,*... in the evening*, and *... at night*. *Rider's British Merlin* almanac for 1795 and a similar almanac for 1773 published in London used them.[12] Other than in English-speaking countries and some Spanish-speaking countries, the terms *a.m.* and *p.m.* are seldom used and often unknown.[α]

### Computer support

In most countries, computers by default show the time in 24-hour notation. Most operating systems, including [Microsoft Windows](/source/Microsoft_Windows) and [Unix-like](/source/Unix-like) systems such as [Linux](/source/Linux) and [macOS](/source/MacOS), activate the 12-hour notation by default for a limited number of language and region settings. This behaviour can be changed by the user, such as with the [Windows](/source/Microsoft_Windows) operating system's "Region and Language" settings.[13]

## Abbreviations

Typical [digital](/source/Digital_clock) 12-hour alarm clock indicating *p.m.* with a dot to the left of the hour.

Typical [analogue 12-hour clock](/source/Clock#Analog)

Main article: [Date and time representation by country](/source/Date_and_time_representation_by_country)

The [Latin](/source/Latin) abbreviations *a.m.* and *p.m.* (often written "am" and "pm", "AM" and "PM", or "A.M." and "P.M.") are used in [English](/source/English_language) (and [Spanish](/source/Spanish_language)).[14][α] 'Noon' is not abbreviated.

When abbreviations and phrases are omitted, one may rely on sentence context and societal norms to reduce ambiguity. For example, if one commutes to work at "9:00", 9:00 a.m. may be implied, but if a [social dance](/source/Social_dance) is scheduled to begin at "9:00", it may begin at 9:00 p.m.

## Related conventions

### Typography

The terms "a.m." and "p.m." are abbreviations of the Latin *ante meridiem* (before midday) and *post meridiem* (after midday). Depending on the [style guide](/source/Style_guide) referenced, the abbreviations "a.m." and "p.m." are variously written in [small capitals](/source/Small_capital) ("am" and "pm"),[16][17] [uppercase](/source/Letter_case) letters without a [period](/source/Full_stop) ("AM" and "PM"), uppercase letters with periods, or lowercase letters ("am" and "pm"[18] or "a.m." and "p.m."[17]).

Some style guides suggest the use of a space between the number and the a.m. or p.m. abbreviation.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] Style guides recommend not using a.m. and p.m. without a time preceding it.[19]

The hour/minute separator [varies between countries](/source/Date_and_time_representation_by_country): some use a colon, others use a period (full stop),[18] and still others use the letter h.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] (In some usages, particularly "[military time](/source/Military_time)", of the [24-hour clock](/source/24-hour_clock), there is no separator between hours and minutes.[20] This style is not generally seen when the 12-hour clock is used.)

### Encoding

[Unicode](/source/Unicode) specifies [codepoints](/source/Codepoint) for *a.m.* and *p.m.* as [precomposed characters](/source/Precomposed_character), which are intended to be used only with [Chinese-Japanese-Korean](/source/CJK_characters) (CJK) character sets, as they take up exactly the same space as one CJK character:

- U+33C2 ㏂ SQUARE AM

- U+33D8 ㏘ SQUARE PM

### Informal speech and rounding off

In speaking, it is common to round the time to the nearest five minutes and/or express the time as the past (or to) the closest hour; for example, "five past five" (5:05). Minutes *past* the hour means those minutes are added to the hour; "ten past five" means 5:10. Minutes *to, till* and *of* the hour mean those minutes are subtracted; "ten of five", "ten till five", and "ten to five" all mean 4:50.

Fifteen minutes is often called a *quarter hour*, and thirty minutes is often known as a *half hour*. For example, 5:15 can be phrased "(a) quarter past five" or "five-fifteen"; 5:30 can be "half past five", "five-thirty" or simply "half five". The time 8:45 may be spoken as "eight forty-five" or "(a) quarter to nine".[21] In some languages, e.g. Polish, rounding off is mandatory when using (spoken) 12-hour clock, but disallowed when using 24 hour notation. I.e. 15:12 might be pronounced as "quarter past three" or "fifteen-twelve", but *not* "three-twelve" or "quarter past fifteen".[22]

In older English, it was common for the number 25 to be expressed as "five-and-twenty".[23] In this way the time 8:35 might have been phrased as "five-and-twenty to 9",[24] although this styling fell out of fashion in the later part of the 1900s and is now rarely used.[25]

Instead of meaning 5:30, the "half five" expression is sometimes used to mean 4:30, or "halfway to five", especially for regions such as the [American Midwest](/source/Midwestern_United_States) and other areas that have been particularly [influenced by German culture](/source/German_America).[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] This meaning follows the pattern choices of many Germanic and [Slavic languages](/source/Slavic_languages), including [Serbo-Croatian](/source/Serbo-Croatian), [Dutch](/source/Dutch_language), [Danish](/source/Danish_language), [Russian](/source/Russian_language), [Norwegian](/source/Norwegian_language), and [Swedish](/source/Swedish_language), as well as [Hungarian](/source/Hungarian_language), [Finnish](/source/Finnish_language), and the languages of the [Baltic States](/source/Baltic_states).

Moreover, in situations where the relevant hour is obvious or has been recently mentioned, a speaker might omit the hour and just say "quarter to (the hour)", "half past" or "ten till" to avoid an elaborate sentence in informal conversations. These forms are often commonly used in television and radio broadcasts that cover multiple time zones at one-hour intervals.[26]

### Formal speech and times to the minute

"O'clock" redirects here. For the o'clock watch, see [O bag](/source/O_bag).

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Minutes may be expressed as an exact number of minutes past the hour specifying the time of day (e.g., 6:32 p.m. is "six thirty-two"). Additionally, when expressing the time using the "past (after)" or "to (before)" formula, it is conventional to choose the number of minutes below 30 (e.g., 6:32 p.m. is conventionally "twenty-eight minutes to seven" rather than "thirty-two minutes past six").

In spoken English, full hours are often represented by the numbered hour followed by [*o'clock*](https://en.wiktionary.org/wiki/o%27clock) (10:00 as *ten o'clock*, 2:00 as *two o'clock*). This may be followed by the "a.m." or "p.m." designator, though some phrases such as *in the morning, in the afternoon, in the evening,* or *at night* more commonly follow analog-style terms such as *o'clock, half past three,* and *quarter to four. O'clock* itself may be omitted, telling a time as *four a.m.* or *four p.m.* Minutes ":01" to ":09" are usually pronounced as *oh one* to *oh nine* (*nought* or *zero* can also be used instead of *oh*). Minutes ":10" to ":59" are pronounced as their usual number-words. For instance, 6:02 a.m. can be pronounced *six oh two a.m.* whereas 6:32 a.m. could be told as *six thirty-two a.m.*.

## Confusion at noon and midnight

Time according to various conventions Device or style Midnight Start of day Noon Midnight End of day Written 24-hour time[27] 00:00 12:00 24:00 or 00:00 of following day U.S. Government Publishing Office (1953)[28] 12 p.m.[a] 12 m. 12 p.m.[a] U.S. Government Publishing Office (2000)[29] 12 p.m.[a] 12 a.m. 12 p.m.[a] U.S. Government Publishing Office (2008)[30] 12 a.m.[a] 12 p.m. 12 a.m.[a] Japanese legal convention[31] 午前0時 (0 a.m.) 午前12時 (12 a.m.) 午後12時 (12 p.m.) Japanese common usage[32] 午前0時 (0 a.m.) 午後0時 (0 p.m.) 午後12時 (12 p.m.) Canadian Press,[33] UK standard[34] midnight noon midnight Associated Press style[35] — noon midnight NIST[2] midnight[b] 12:01 a.m. noon midnight[b] 11:59 p.m. ^ a b c d e f These styles are ambiguous with respect to whether midnight is at the start or end of each day. ^ a b NIST recommends using 11:59 p.m. and 12:01 a.m. to disambiguate when needed.

It is not always clear what times "12:00 a.m." and "12:00 p.m." denote. In [Latin](/source/Latin), **ante meridiem** (a.m.) means "before midday" and **post meridiem** (p.m.) means "after midday". Since noon is neither before nor after itself, the terms a.m. and p.m. do not apply.[2] Although noon could be denoted "12 m.", this is seldom done[36] and also does not resolve the question of how to indicate midnight.

By convention, "12 a.m." denotes midnight and "12 p.m." denotes noon.[37] However, many style guides recommend against using either because of the potential for confusion. Many recommend instead using the unambiguous terms "12 noon" and "12 midnight", or simply "noon" and "midnight". These include *[The American Heritage Dictionary of the English Language](/source/The_American_Heritage_Dictionary_of_the_English_Language)*,[37] *The Canadian Press Stylebook*,[33] and the [NIST](/source/National_Institute_of_Standards_and_Technology)'s "Frequently asked questions (FAQ)" web page.[2]

Alternatively, some recommend referring to one minute before or after 12:00, especially when referring to midnight (for example, "11:59 p.m." or "12:01 a.m."). These include the UK's [National Physical Laboratory](/source/National_Physical_Laboratory_(United_Kingdom)) "FAQ-Time" web page.[34] That has become common in the United States in legal contracts and for [airplane](/source/Airplane), [bus](/source/Bus), or [train](/source/Train) schedules, though some schedules use other conventions. Occasionally, when trains run at regular intervals, the pattern may be broken at midnight by displacing the midnight departure one or more minutes, such as to 11:59 p.m. or 12:01 a.m.[38]

Some authors have been known to use the reverse of the normal convention. E. G. Richards in his book *Mapping Time* (1999) provided a diagram in which 12 a.m. means noon and 12 p.m. means midnight.[39] Historically, the style manual of the [United States Government Printing Office](/source/United_States_Government_Printing_Office) used 12 a.m. for noon and 12 p.m. for midnight, though this was reversed in its 2008 editions.[29][30]

## See also

- [24-hour clock](/source/24-hour_clock) – Timekeeping convention

- [Canonical hours](/source/Canonical_hours) – Christian concept of periods of prayer throughout the day

- [Clock position](/source/Clock_position) – Relative direction using a dial

- [Date and time representation by country](/source/Date_and_time_representation_by_country)

- [Decimal time](/source/Decimal_time) – Time of day using decimal units

- [Italian six-hour clock](/source/Italian_six-hour_clock) – Historic timekeeping system

- [Midnight](/source/Midnight) – Transition time from one day to the next

- [Muhurta](/source/Muhurta) – Time of the day as benefic or malefic

- [Noon](/source/Noon) – 12 o'clock in the daytime

- [Pahar](/source/Pahar) – Unit of time used in Indian subcontinent

- [Thai six-hour clock](/source/Thai_six-hour_clock) – Thai timekeeping system

## Notes

1. ^ [***a***](#cite_ref-Other_14-0) [***b***](#cite_ref-Other_14-1) The equivalents in [Greek](/source/Greek_language) are π.μ. and μ.μ., respectively, and in [Sinhala](/source/Sinhala_language) පෙ.ව. (**pe.va.**) for පෙරවරු (**peravaru**, පෙර **pera** – fore, pre) and ප.ව. (**pa.va.**) for පස්වරු (**pasvaru**, පස්සේ **passē** – after, post). In [Irish](/source/Irish_language), *a.m.* and *i.n.* are used, standing for *ar maidin* ("in the morning") and *iarnóin* ("afternoon") respectively. In Portuguese, there are two official options and many others used, for example, using 21:45, 21h45 or 21h45min (official ones) or 21:45 or 9:45 p.m. Most other languages lack formal abbreviations for "before noon" and "after noon", and their users use the 12-hour clock only orally and informally.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] In those languages, such as Polish, Russian, and Hebrew, 24-hour clock is always used in writing, even informal writing, though 12-hour designations may be used colloquially in speech, such as "9 in the morning" or "3 in the night".[15] In those languages, an email saying "let's meet at 15:00" might be read out aloud as "let's meet at three in the afternoon".

## References

1. ^ [***a***](#cite_ref-EncyclopaediaBritannica_1-0) [***b***](#cite_ref-EncyclopaediaBritannica_1-1) "Time". *The New Encyclopædia Britannica*. Vol. 28. 1986. pp. 660 2a. ["Time"](http://library.eb.com.au/eb/article-61027). *Encyclopædia Britannica. Encyclopædia Britannica Online Library Edition*. Retrieved 20 November 2013. The use of AM or PM to designate either noon or midnight can cause ambiguity. (subscription required)

1. ^ [***a***](#cite_ref-NISTFAQ_2-0) [***b***](#cite_ref-NISTFAQ_2-1) [***c***](#cite_ref-NISTFAQ_2-2) [***d***](#cite_ref-NISTFAQ_2-3) ["Times of Day FAQs"](https://www.nist.gov/pml/time-and-frequency-division/times-day-faqs). [National Institute of Standards and Technology](/source/National_Institute_of_Standards_and_Technology). 21 September 2016. [Archived](https://web.archive.org/web/20180921153333/https://www.nist.gov/pml/time-and-frequency-division/times-day-faqs) from the original on 21 September 2018. Retrieved 30 September 2018.

1. **[^](#cite_ref-3)** Addington, Susan (25 August 2016). ["Modular Arithmetic"](https://web.archive.org/web/20080704121745/http://www.math.csusb.edu/faculty/susan/number_bracelets/mod_arith.html). Archived from [the original](http://www.math.csusb.edu/faculty/susan/number_bracelets/mod_arith.html) on 4 July 2008. Retrieved 28 November 2008.

1. **[^](#cite_ref-4)** ["Is noon 12 am or 12 pm?"](https://www.rmg.co.uk/stories/topics/noon-12-am-or-12-pm). *Royal Museums Greenwich*. Retrieved 26 January 2023.

1. **[^](#cite_ref-5)** ["U.S. Government Printing Office Style Manual - Chapter 12 - Numerals"](https://www.govinfo.gov/content/pkg/GPO-STYLEMANUAL-2008/html/GPO-STYLEMANUAL-2008-14.htm). *govinfo.gov*. Retrieved 27 January 2023.

1. **[^](#cite_ref-6)** ["time of day, elapsed time"](https://www.noslangues-ourlanguages.gc.ca/en/writing-tips-plus/time-of-day-elapsed-time). *Resources of the Language Portal of Canada*. 22 October 2020. Retrieved 27 January 2023.

1. **[^](#cite_ref-8)** ["The History of Clocks"](https://web.archive.org/web/20081013135550/http://www.arcytech.org/java/clock/clock_history.html). 13 October 2008. Archived from [the original](http://www.arcytech.org/java/clock/clock_history.html) on 13 October 2008. Retrieved 12 November 2017.

1. **[^](#cite_ref-9)** ["Berlin instruments of the old Eg.time of day destination"](http://members.aon.at/sundials/berlin-egypte.htm). *members.aon.at*. [Archived](https://web.archive.org/web/20061115233642/http://members.aon.at/sundials/berlin-egypte.htm) from the original on 15 November 2006. Retrieved 13 June 2006.

1. **[^](#cite_ref-10)** ["Early Clocks"](https://www.nist.gov/pml/time-and-frequency-division/popular-links/walk-through-time/walk-through-time-early-clocks). *A Walk Through Time*. [National Institute of Standards and Technology](/source/National_Institute_of_Standards_and_Technology). 12 August 2009.

1. **[^](#cite_ref-11)** Bartels, Meghan (20 February 2017). ["Early Tech Adopters in Ancient Rome Had Portable Sundials"](https://www.smithsonianmag.com/innovation/early-tech-adopters-ancient-rome-had-portable-sundials-180962225/). *Smithsonian Magazine*. Retrieved 8 March 2025.

1. **[^](#cite_ref-12)** ["Timekeeping In the Roman army"](https://www.thehourglass.com/story/timekeeping-in-the-roman-army). 7 July 2018.

1. **[^](#cite_ref-13)** [*National Library of Australia catalogue entry for*Rider's British merlin: for the year of Our Lord God 1795](http://catalogue.nla.gov.au/Record/4881611). Printed for the Company of Stationers, and sold by R. Horsfield, at Stationers-hall, near Ludgate-street. 1795. [Archived](https://web.archive.org/web/20130522172644/http://catalogue.nla.gov.au/Record/4881611) from the original on 22 May 2013.

1. **[^](#cite_ref-15)** Lawrence Abrams (13 December 2012). ["How to customize how the time is displayed in Windows"](http://www.bleepingcomputer.com/tutorials/customize-how-time-is-displayed-in-windows/). Bleeping Computer. [Archived](https://web.archive.org/web/20131029183705/http://www.bleepingcomputer.com/tutorials/customize-how-time-is-displayed-in-windows/) from the original on 29 October 2013. Retrieved 26 October 2013.

1. **[^](#cite_ref-16)** ["hora"](http://buscon.rae.es/dpdI/SrvltGUIBusDPD?lema=hora2). *Diccionario panhispánico de dudas* (in Spanish). [Archived](https://web.archive.org/web/20110720024649/http://buscon.rae.es/dpdI/SrvltGUIBusDPD?lema=hora2) from the original on 20 July 2011.

1. **[^](#cite_ref-17)** ["Jak poprawnie zapisywać daty i inne określenia czasu?"](https://synomix.pl/jak-poprawnie-zapisywac-daty-i-inne-okreslenia-czasu) [How do I correctly write dates and other time expressions?] (in Polish). Retrieved 18 March 2025.

1. **[^](#cite_ref-18)** Trask, Larry. ["Small Capitals"](https://www.sussex.ac.uk/informatics/punctuation/misc/small). *University of Sussex Informatics*. The University of Sussex. Retrieved 30 October 2024.

1. ^ [***a***](#cite_ref-Chicago_MOS_19-0) [***b***](#cite_ref-Chicago_MOS_19-1) ["9.39: Numerals versus words for time of day"](https://www.chicagomanualofstyle.org/book/ed18/part2/ch09/psec039.html). *The Chicago Manual of Style Online*. The University of Chicago. Retrieved 30 October 2024.

1. ^ [***a***](#cite_ref-ESG_20-0) [***b***](#cite_ref-ESG_20-1) *Economist Style Guide* (12th ed.). [The Economist](/source/The_Economist). 2018. p. 185. [ISBN](/source/ISBN_(identifier)) [9781781258316](https://en.wikipedia.org/wiki/Special:BookSources/9781781258316).

1. **[^](#cite_ref-21)** Hacker, Diana, A Writer's Reference, six edition, Bedford, St Martin's, Boston, 2007, section M4-c, p.308.

1. **[^](#cite_ref-22)** [*The Tongue and Quill*](https://web.archive.org/web/20201126183321/https://static.e-publishing.af.mil/production/1/saf_cn/publication/afh33-337/afh33-337.pdf) (PDF). US Air Force. 27 May 2015. p. 356. Archived from [the original](https://static.e-publishing.af.mil/production/1/saf_cn/publication/afh33-337/afh33-337.pdf) (PDF) on 26 November 2020. Retrieved 26 October 2021. Air Force Handbook 33-337.

1. **[^](#cite_ref-23)** "quarter". *American Heritage Dictionary* (3rd ed.). Boston: Houghton Mifflin. 1992. s.v. usage note at end of "quarter" entry.

1. **[^](#cite_ref-24)** ["Określanie godzin i minut"](https://sjp.pwn.pl/poradnia/haslo/Okreslanie-godzin-i-minut;19024.html). *Słownik języka polskiego PWN* (in Polish). Retrieved 18 March 2025.

1. **[^](#cite_ref-25)** Dickens, Charles (1855). *Little Dorrit*. p. Chapter 27.

1. **[^](#cite_ref-26)** Trudgill, Peter (17 May 2020). ["Number five-and-twenty: A fading linguistic practice"](https://www.theneweuropean.co.uk/brexit-news-peter-trudgill-recounts-the-old-way-of-counting-80170/). *The New European*. Retrieved 13 October 2022.

1. **[^](#cite_ref-27)** Swan, Michael. ["Ask About English"](https://www.bbc.co.uk/worldservice/learningenglish/radio/specials/1535_questionanswer/page63.shtml). *BBC World Service*. BBC. Retrieved 13 January 2021.

1. **[^](#cite_ref-28)** ["TVTimes magazine 21-27 May 1983 part1"](http://forums.doyouremember.co.uk/threads/8061-TVTimes-magazine-21-27-May-1983-part1). *TVTimes*. 21–27 May 1983. [Archived](https://web.archive.org/web/20121018072904/http://forums.doyouremember.co.uk/threads/8061-TVTimes-magazine-21-27-May-1983-part1) from the original on 18 October 2012. Retrieved 8 October 2019.

1. **[^](#cite_ref-29)** *Chicago Manual of Style* (18th ed.). University of Chicago Press. 2024. paragraph 9.41. [ISBN](/source/ISBN_(identifier)) [978-0-226-81797-2](https://en.wikipedia.org/wiki/Special:BookSources/978-0-226-81797-2).

1. **[^](#cite_ref-GPO1953_30-0)** ["United States Government Printing Office Style Manual"](https://www.govinfo.gov/content/pkg/GOVPUB-GP-6eda8715b8f5cb1d8514325b97334d4f/pdf/GOVPUB-GP-6eda8715b8f5cb1d8514325b97334d4f.pdf) (PDF). *govinfo*. U.S. Government Publishing Office. January 1953. pp. 152, 267. [Archived](https://web.archive.org/web/20190905161607/https://www.govinfo.gov/content/pkg/GOVPUB-GP-6eda8715b8f5cb1d8514325b97334d4f/pdf/GOVPUB-GP-6eda8715b8f5cb1d8514325b97334d4f.pdf) (PDF) from the original on 5 September 2019. Retrieved 5 September 2019.

1. ^ [***a***](#cite_ref-GPO2000_32-0) [***b***](#cite_ref-GPO2000_32-1) ["U.S. Government Printing Office Style Manual"](https://www.govinfo.gov/content/pkg/GPO-STYLEMANUAL-2000/pdf/GPO-STYLEMANUAL-2000.pdf) (PDF). *govinfo*. U.S. Government Publishing Office. 2000. page 156. [Archived](https://web.archive.org/web/20190905160112/https://www.govinfo.gov/content/pkg/GPO-STYLEMANUAL-2000/pdf/GPO-STYLEMANUAL-2000.pdf) (PDF) from the original on 5 September 2019. Retrieved 5 September 2019.

1. ^ [***a***](#cite_ref-GPO2008_33-0) [***b***](#cite_ref-GPO2008_33-1) ["U.S. Government Printing Office Style Manual"](https://www.govinfo.gov/content/pkg/GPO-STYLEMANUAL-2008/pdf/GPO-STYLEMANUAL-2008.pdf) (PDF). *govinfo*. U.S. Government Publishing Office. 2008. p. 271. [Archived](https://web.archive.org/web/20190412235057/https://www.govinfo.gov/content/pkg/GPO-STYLEMANUAL-2008/pdf/GPO-STYLEMANUAL-2008.pdf) (PDF) from the original on 12 April 2019. Retrieved 5 September 2019.

1. **[^](#cite_ref-34)** [午前１２時？ 午後０時？](https://web.archive.org/web/20170606032129/http://jjy.nict.go.jp/QandA/FAQ/12am-or-0pm-J.html) [12 AM? or 0 PM?]. *[National Institute of Information and Communications Technology](/source/National_Institute_of_Information_and_Communications_Technology)* (in Japanese). 15 February 1989. Archived from [the original](http://jjy.nict.go.jp/QandA/FAQ/12am-or-0pm-J.html) on 6 June 2017. Retrieved 24 May 2017.

1. **[^](#cite_ref-NAO_Japan_35-0)** [質問4-1）正午は午前12時？それとも、午後12時？](https://www.nao.ac.jp/faq/a0401.html) [Question 4-1) Is noon 12 a.m.? Or 12 p.m.?]. *[National Astronomical Observatory of Japan](/source/National_Astronomical_Observatory_of_Japan)* (in Japanese). Retrieved 19 January 2022.

1. ^ [***a***](#cite_ref-CP_36-0) [***b***](#cite_ref-CP_36-1) *The Canadian Press Stylebook* (11th ed.). 1999. page 288.

1. ^ [***a***](#cite_ref-NPL_37-0) [***b***](#cite_ref-NPL_37-1) ["National Physical Laboratory, *FAQ-Time*"](https://web.archive.org/web/20150303095129/http://www.npl.co.uk/science-technology/time-frequency/time/faqs/). Archived from [the original](http://www.npl.co.uk/science-technology/time-frequency/time/faqs) on 3 March 2015. Retrieved 11 January 2015.

1. **[^](#cite_ref-AP_38-0)** Paula Froke, Anna Joe Bratton, Oskar Garcia, Jeff McMillan & Jerry Schwart, Eds., 54th ed., *The Associated Press Stylebook and Briefing on Media Law*, New York: Basic Books, June 2019, [ISBN](/source/ISBN_(identifier)) [978-1-5416-9989-2](https://en.wikipedia.org/wiki/Special:BookSources/978-1-5416-9989-2), s.v. noon, midnight, times.

1. **[^](#cite_ref-chicago_40-0)** *Chicago Manual of Style* (18th ed.). University of Chicago Press. 2024. paragraph 9.40. [ISBN](/source/ISBN_(identifier)) [978-0-226-81797-2](https://en.wikipedia.org/wiki/Special:BookSources/978-0-226-81797-2). Although noon can be expressed as 12:00 m. (m = *meridies*), very few use that form.

1. ^ [***a***](#cite_ref-AHDEL_41-0) [***b***](#cite_ref-AHDEL_41-1) ["AM"](http://ahdictionary.com/word/search.html?q=AM). *[The American Heritage Dictionary of the English Language](/source/The_American_Heritage_Dictionary_of_the_English_Language)* (Fifth ed.). 2011. [Archived](https://web.archive.org/web/20140109230904/http://ahdictionary.com/word/search.html?q=AM) from the original on 9 January 2014.

1. **[^](#cite_ref-42)** ["Cheshunt/Enfield Town to London Liverpool Street via Seven Sisters service Interim train timetables"](https://web.archive.org/web/20150526154117/http://www.abelliogreateranglia.co.uk/f/62130/62130.pdf) (PDF). *Abellio Greater Anglia London*. 17 May 2015. pp. 7, 8. Archived from [the original](http://www.abelliogreateranglia.co.uk/f/62130/62130.pdf) (PDF) on 26 May 2015.

1. **[^](#cite_ref-43)** Richards, E. G. (1999). *Mapping Time: the Calendar and its History*. [Oxford University Press](/source/Oxford_University_Press). p. 289.

## External links

- [NIST FAQ on time](https://www.nist.gov/pml/div688/times.cfm) [Archived](https://web.archive.org/web/20120916120545/http://www.nist.gov/pml/div688/times.cfm) 16 September 2012 at the [Wayback Machine](/source/Wayback_Machine)

- [12am is noon in Japan](https://longtailworld.blogspot.com/2006/04/japan1212am-is-noon-in-japan.html)

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Adapted from the Wikipedia article [12-hour clock](https://en.wikipedia.org/wiki/12-hour_clock) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/12-hour_clock?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.