The 24-hour clock, also referred to (only in the US) as military time or (only in the United Kingdom and now very rarely) as continental time is a convention of time-keeping in which the day runs from midnight to midnight and is divided into 24 hours, numbered from 0 to 23. A time in the 24-hour clock is written in the form hours:minutes (for example, 01:23), or hours:minutes:seconds (01:23:45). Under the 24-hour clock system, the day begins at midnight, 00:00, and the last minute of the day is that beginning at 23:59. To convert between the 12-hour clock and the 24-hour clock, use the table to the right. The vast majority of the French population use this system when talking casually.

The 24-hour clock has a number of advantages over the 12-hour system:

• There is no possibility of ambiguity between times in the morning and evening (in the 12-hour system "seven o'clock" means both 7 am and 7 pm), and in reading schedules and the like it is easy to see at a glance whether times refer to before or after noon. This is especially important for organizations that run services 24 hours a day, such as airlines, railways, and the military.
• The 12-hour clock often writes noon as 12 pm and midnight as 12 am: a convention which is ambiguous and confuses many people. The 24-hour clock notates noon as 12:00, and midnight as 00:00 on the following day.

However, opening hours etc. until midnight usually use "24:00", e.g. "0:00–24:00", "7:00–24:00". Also the notation 24:00 is used for example in railway timetables, to indicate the end of the day. Thus a train due to arrive at a station during the last minute of any particular day may be shown as doing so at 24:00; trains due to depart during the first minute of the day are shown as leaving at 00:00.

As well as military, public safety, and transport applications, the 24-hour clock also enjoys broad everyday civilian usage in many Asian, European and Latin American countries, and is widely used in establishing settings for computer operating systems. Many models of digital wristwatches and clocks are available that display the time of day using the 24-hour clock.

See also

• 12-hour clock
• Zulu time
• fencepost error
• Clock
• Decimal time
• ISO 8601
• Boundaries of the day