24-hour clock facts for kids

The 24-hour clock is a way to tell time that uses all 24 hours in a day. Unlike the 12-hour clock system, it does not use "a.m." or "p.m." to show if it's morning or afternoon. Instead, the hours are numbered from 0 to 23.

This system is often called military time in the United States and parts of Canada. In other places, it might be known as railway time or continental time. It's also the standard way time is written internationally (ISO 8601).

When you write time using the 24-hour clock, it usually looks like hours:minutes, for example, 01:23. If the hour or minute is less than 10, a zero is put in front, like 09:07.

The day starts at midnight, which is 00:00. The last minute of the day starts at 23:59. The very end of the day can be called 24:00, which is the same as 00:00 of the next day. For example, "Tuesday at 24:00" means the same moment as "Wednesday at 00:00." However, the US military usually says "23:59" instead of "24:00" to avoid having two names for the same time.

Understanding the 24-Hour Clock

The 24-hour clock counts hours from 0 to 23. This means that after 12:00 noon, the numbers keep going up. For example, 1 p.m. becomes 13:00, 2 p.m. becomes 14:00, and so on.

Converting to 24-Hour Time

To change a 12-hour time to a 24-hour time:

• For times from 1 a.m. to 12:59 p.m., the hour stays the same. For example, 9:00 a.m. is 09:00.
• For times from 1 p.m. to 11:59 p.m., you add 12 to the hour. For example, 3:00 p.m. is 15:00 (3 + 12 = 15).
• Midnight (12:00 a.m.) is 00:00.
• Noon (12:00 p.m.) is 12:00.

Where is the 24-Hour Clock Used?

The 24-hour clock is used in many important areas because it helps avoid confusion.

• Computers and digital systems often use it.
• The military and public safety services (like police and fire departments) use it to be very clear about times.
• Transport systems, such as trains and airplanes, rely on it for schedules.
• Many countries in Asia, Europe, and Latin America use the 24-hour clock for writing and sometimes speaking about time.
• Many digital watches and clocks also show time in this format.

For example, in railway timetables, 24:00 means the end of a day. A train arriving at 24:00 is arriving at the very last minute of that day. But a train leaving at 00:00 is leaving at the very first minute of the next day.

You might also see it for shop opening hours, like "07:00–24:00," meaning the shop is open from 7 a.m. until midnight.

Why Use the 24-Hour Clock?

There are several good reasons why the 24-hour clock is helpful:

• Less Confusion: It's much clearer if a time is morning or evening. For example, 7 o'clock in the evening is always 19:00, so there's no mix-up with 7:00 a.m.
• No A.M. or P.M.: You don't need to remember if noon is 12 a.m. or 12 p.m.
• Easier Calculations: It can be simpler to figure out how long something lasts. If an event starts at 14:00 and ends at 17:00, you can quickly see it's 3 hours long (17 - 14 = 3).

Images for kids

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  24-hour digital clock in Miaoli HSR station.

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  24-hour clock as seen on the USS Midway.

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  Paolo Uccello's Face with Four Prophets/Evangelists (1443) in the Florence Cathedral

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  The 24-hour tower clock in Venice that lists hours 1 to 12 twice

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  The Shepherd Gate Clock with Roman numerals up to XXIII (23) and 0 for midnight, in Greenwich

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  A Russian 24-hour watch for polar expeditions from 1969, made by Soviet watchmaker Raketa.

See also

In Spanish: Sistema horario de 24 horas para niños