Two ways to tell time
The 12-hour system uses a.m. (midnight to noon) and p.m. (noon to midnight). The 24-hour system counts the hours from 0000 to 2359, with no a.m. or p.m.
Key idea
For p.m. times, add 12 to the hour. For a.m. times, keep the same hour (write two digits).
Changing between them
Worked example
3:00 p.m. → add 12 to the hour: 3 + 12 = 15 → 1500 hours.
0900 hours → 9 is before noon → 9:00 a.m.
Special times: 12:00 midnight = 0000 hours, and 12:00 noon = 1200 hours.
Remember
- p.m. hour + 12 = 24-hour time.
- 24-hour times always have 4 digits.
- a.m. hours stay the same number.