How the 24-hour clock works
The 24-hour clock counts the hours of the day from 00 at midnight to 23, with no AM or PM. The 12-hour clock counts from 1 to 12 twice and adds AM (before noon) or PM (after noon).
The 24-hour clock is used for flights, transport, software and official schedules because it cannot confuse morning and evening.
Conversion rule
| 24-hour | Rule | Example |
|---|---|---|
| 00 | Midnight = 12 AM | 00:30 = 12:30 AM |
| 01–11 | Unchanged, AM | 09:15 = 9:15 AM |
| 12 | Noon = 12 PM | 12:45 = 12:45 PM |
| 13–23 | Subtract 12, PM | 20:00 = 8:00 PM |
To convert back, add 12 to PM hours from 1 to 11, and make 12 AM equal 00.
Related tools
To measure the time between two clock times or add hours to a time, use the Hours Calculator; for today’s date on both calendars, see Today’s date.
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