How to Read a 24-Hour Clock

The 24-hour clock — also called military time in the United States — represents every hour of the day as a number from 00 to 23, eliminating the need for AM and PM. It is the standard in aviation, the military, hospitals, science, and most of the world outside North America. Once you understand the pattern, converting between 12-hour and 24-hour time takes only a few seconds.

The basic rules

• Midnight is 00:00 (sometimes written as 0000 in military time)
• Morning hours (1 AM–12 PM) are the same as 12-hour time with a leading zero: 1 AM = 01:00, 9 AM = 09:00, 11 AM = 11:00
• Noon is 12:00 — same in both systems
• Afternoon and evening (1 PM–11 PM) add 12 to the hour: 1 PM = 13:00, 6 PM = 18:00, 11 PM = 23:00
• The day ends at 23:59 — one minute before midnight

The quick conversion trick

For PM times after noon, just add 12 to the hour:

• 1 PM → 1 + 12 = 13:00
• 3 PM → 3 + 12 = 15:00
• 7 PM → 7 + 12 = 19:00
• 10 PM → 10 + 12 = 22:00

To go the other way — converting 24-hour time back to PM — subtract 12 from any hour above 12:

• 14:00 → 14 − 12 = 2:00 PM
• 17:30 → 17 − 12 = 5:30 PM
• 21:45 → 21 − 12 = 9:45 PM

Full conversion table

Where the 24-hour clock is used

• Aviation: All flight schedules and air traffic control worldwide use 24-hour UTC time.
• Military: Used by armed forces in most countries to avoid AM/PM ambiguity in operations. In the US military, it is spoken without a colon: “1430” is said “fourteen thirty.”
• Healthcare: Hospital records, medication schedules, and medical notes use 24-hour time to prevent dangerous AM/PM errors.
• Computing and software: Servers, databases, and log files almost always use 24-hour UTC timestamps.
• Most of the world: Europe, Latin America, Asia, Africa, and Australia predominantly use 24-hour clocks in daily life. The 12-hour clock is mainly a North American and some Commonwealth convention.

The two special cases to remember

Two times cause the most confusion:

• Midnight:In 12-hour time, midnight is 12:00 AM. In 24-hour time, it is 00:00. The day starts at 00:00 and the previous day ended at 23:59. Some systems also write midnight as 24:00 to mean “the end of the day” rather than “the start,” but 00:00 is more common.
• Noon: In 12-hour time, noon is 12:00 PM. In 24-hour time, it is also 12:00. Noon is the one time where both systems agree exactly.