| clock system | |
|---|---|
| 12-hour | 24-hour |
| midnight 12:00 a.m.* | 00:00 |
| 1:00 a.m. | 01:00 |
| 2:00 a.m. | 02:00 |
| 3:00 a.m. | 03:00 |
| 4:00 a.m. | 04:00 |
| 5:00 a.m. | 05:00 |
| 6:00 a.m. | 06:00 |
| 7:00 a.m. | 07:00 |
| 8:00 a.m. | 08:00 |
| 9:00 a.m. | 09:00 |
| 10:00 a.m. | 10:00 |
| 11:00 a.m. | 11:00 |
| noon 12:00 p.m.* | 12:00 |
| 1:00 p.m. | 13:00 |
| 2:00 p.m. | 14:00 |
| 3:00 p.m. | 15:00 |
| 4:00 p.m. | 16:00 |
| 5:00 p.m. | 17:00 |
| 6:00 p.m. | 18:00 |
| 7:00 p.m. | 19:00 |
| 8:00 p.m. | 20:00 |
| 9:00 p.m. | 21:00 |
| 10:00 p.m. | 22:00 |
| 11:00 p.m. | 23:00 |
| undefined (midnight)* | 24:00 |
| * See section "Confusion at noon and midnight" | |
The 12-hour clock is a timekeeping convention in which the 24 hours of the day are divided into two periods called ante meridiem (a.m., Latin "before noon") and post meridiem (p.m., "after noon"). Each period consists of 12 hours numbered 12 (acting as zero), 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. The indication of noon and midnight in the 12-hour system is disputed.
The 12-hour clock was developed over time from the mid-second millennium BC, to the 16th century A.D. and was once popular throughout Northern Europe, but is now the dominate system used only in a few former British and American Colonies. It is also used informally in most of the world. The notion has received much criticism, yet survives out of tradition.
