24-hour time explained

By Adam Gouda · Last reviewed November 9, 2026

The 24-hour clock numbers the hours of the day from 00 to 23 instead of repeating 1 to 12 with a.m. and p.m. It’s the standard in most of the world, and in aviation, the military, medicine and transportation, because it removes any chance of confusing morning and evening. In the U.S. it’s often called “military time.”

How to convert

• From midnight to 12:59 p.m.: the hour stays the same, except 12 a.m. becomes 00. So 9:15 a.m. is 09:15.
• From 1:00 p.m. to 11:59 p.m.: add 12 to the hour. So 3:40 p.m. is 15:40.
• Going back: if the hour is 13 or more, subtract 12 and add “p.m.”

Conversion chart

How to say it

• In military and aviation use, times are spoken as four digits: 0600 is “zero six hundred” and 1430 is “fourteen thirty.”
• Whole hours are “hundred”: 1900 is “nineteen hundred.” It’s never “nineteen hundred hours” and “o’clock” together.
• With a time zone letter: 1430Z is “fourteen thirty Zulu.”

Midnight and noon

Midnight at the start of a day is 00:00. Some schedules write the end of a day as 24:00, which is the same instant as 00:00 the next day. To avoid confusion, many timetables use 23:59 or 00:01 instead. Noon is simply 12:00, which avoids the ambiguous “12 a.m. or 12 p.m.?” question.

Switch formats on the clock

Use the 12 H / 24 H toggle at the top of the Global Flight Clock to switch every city between formats. The Zulu strip always shows 24-hour UTC, the way it’s used in aviation.

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