24-hour count

from Wikipedia, the free encyclopedia
24-hour count 2 times 12 hour count
00:00 12:00 a. m. / midnight *
00:01 12:01 a. m. ( ante meridiem )
01:00 01:00 a. m.
02:00 02:00 a. m.
... ...
10:00 10:00 a. m.
11:00 11:00 a. m.
11:59 11:59 a. m. ( ante meridiem )
12:00 12:00 p. m. / noon *
12:01 pm 12:01 p. m. ( post meridiem )
13:00 01:00 p. m.
14:00 02:00 p. m.
... ...
22:00 10:00 p. m.
23:00 11:00 p. m.
23:59 11:59 p. m. ( post meridiem )
24:00 ** 12:00 a. m. / midnight
*Since 12 a. m. and 12 p. m. are easily confused, noon or midnight is often preferred in English .
** Rare
Greenwich Observatory 24 hour clock

The 24-hour counting (or astronomical counting of the hours ) is the most widely used form in which the hours are given today. Another form of time is 2 times 12 hours .


The counting takes place in 24 equinoxed hours of equal length, into which the full day (the clear day and the night ) are divided together. The so-called big clock counts continuously from the first (1st) to the 24th hour. The time for the first (1st) hour ranges from 12:00 a.m. to 1:00 a.m., and for the 24th hour from 11:00 p.m. to 12:00 a.m. Counting starts at midnight , but the counting changes from 11:59 p.m. directly to 0:00 a.m. of the following day, there is no, even logical second, between the two minutes.


Long before the Middle Ages, 24-hour counting was in use, but it usually began with sunrise ( Babylonian or Greek hours ), and occasionally after sunset ( Italian or Bohemian hours ). The 24-hour counting spread in learned circles since the late Middle Ages , when, with the advent of mechanical clocks, the separate counting of day and night with 12 temporal hours of unequal length each posed a technical problem. However, only a few people owned such clocks, so that the old hour counting was in many cases still in use until the 18th century. There were also differences between town and country.

For practical reasons, even after the spread of mechanical clocks and the abandonment of day and night hours, which vary depending on the season, in the public area, the traditional, separate 12-hour counting for day and night times remained, although the mechanically measured hours are now always the same were long and the transition from day to night counting no longer coincided with the onset of dusk. Accordingly, in the 15th century, the so-called “small clock” with double hour counting became established. This clock makes two revolutions every 24 hours and shows two different ones of the 24 hours of the full day at every point on the dial: 1 o'clock and 1 o'clock with "I"; 12 noon and midnight with "XII". Double counting is known as the 2-by-12-hour count, or 12-hour count for short .

The reasons for this development can be named:

  • The first public mechanical clocks were striking tower clocks that did not yet show the time of day . These acoustic clocks never used more than twelve sound signals because so many tower clock strikes were not meaningful to count.
  • The small mechanical watch was easier to construct than the "big watch" and was designed to last longer.
Railway pocket watch with 24-hour dial (from 1927, Germany)

For rail traffic , travel times and timetables were easier to create and communicate with the 24-hour counter. The military, too, was keen to avoid confusion when communicating times and used this counting method early on. At the turn of the 19th to the 20th century, the 24-hour counting was therefore introduced in many countries:

The British and Canadian military used the 24-hour counting from late 1917. In many of the countries mentioned, both counting systems have existed and have existed side by side for a long time.

The 24-hour counting is now the standardized time counting of the ISO ( ISO 8601 ). This system has prevailed in most countries in the world.

12 versus 24 hours

The 12-hour counting is still used today in writing in public life in parts of the English-speaking world, as well as in all of Latin America and the Philippines , usually with the addition a. m. respectively p. m. for “morning” and “afternoon”. In many European countries, too, it is still dominant in everyday oral language. In German, for example, the regionally different expressions for started hours (for example, “half past three” for 3:30 p.m.) are only associated with the 12-hour counting method and not with a 24-hour counting.

The 24-hour counting has special names in some regions where the 12-hour counting is preferred:

  • military time in Canada and the USA ,
  • army time in australia ,
  • railway time or radio time in various parts of the English-speaking world,
  • horario ferroviario or horario continental in parts of the Spanish-speaking world.

With the advent of digital clocks , the 24-hour counting system became increasingly popular in everyday life. Pointer watches with a 24-hour display are rare. In regions of the world where 24-hour counting is uncommon, digital clocks also show 12 hours twice.

Times after 24:00

Danish ticket with the non-standard time of 27:18

Times of the day after 24:00 (e.g. 24:01 or 25:59 instead of 00:01 or 01:59) are not used frequently and are not subject to the standard. However, these notations also exist in certain circumstances in the United Kingdom , Japan , South Korea , China and Hong Kong , where business hours are extended until after midnight , such as for television and cinema. At the companies of the Hamburger Verkehrsverbund , which used TIM printers , it was customary for tickets issued after midnight to continue turning the time until the end of the working day. B. to print out with the time 24:40.

See also


  • Karl Walbrach: A question of time. In: Lok Magazin . 7/2002, pp. 114-117.

Web links

Commons : 24 hour counting  - collection of pictures, videos and audio files

Individual evidence

  1. AM . In: American Heritage® Dictionary of the English Language . 5th edition. Houghton Mifflin Harcourt, 2011 ( ahdictionary.com ).
  2. BGH, decision of VI. Civil Senate of May 8, 2007 - VI ZB 74/06 - = NJW 2007, 2045 = MDR 2007, 1093.
  3. Jörg Meyer: The sundial and its theory. Harry Deutsch, 2008, ISBN 978-3-8171-1824-3 , p. 100.
  4. Walbrach, p. 115.
  5. Overview of the history of the German railways 1835–1999 on railforum.de Walbrach, p. 116.