Understand the idea.
Read the hour before changing it
A 24-hour clock counts hours from midnight instead of starting again after noon. For 1 pm to 11 pm, add 12 to the hour; morning hours 1 am to 11 am keep their number. Minutes stay unchanged.
Treat the two 12s separately: 12 am begins the day at 00:00, while 12 pm is noon at 12:00. For example, 12:25 am becomes 00:25, but 12:25 pm remains 12:25. Write a leading zero for a single-digit hour.
| 12-hour time | 24-hour time |
|---|---|
| Midnight | 00:00 |
| 7:05 am | 07:05 |
| Noon | 12:00 |
| 6:40 pm | 18:40 |
Convert back and check the part of day
To return to 12-hour time, hours 13 to 23 become pm after subtracting 12. Hours 01 to 11 become am. Hour 00 becomes 12 am, and hour 12 becomes 12 pm; neither follows the subtraction rule.
Check that the answer describes the same part of the day. A 21:10 departure is in the evening, so it must become 9:10 pm. Always include am or pm in a 12-hour answer because the same clock reading occurs twice daily.
See the method in action.
Evening to 24-hour time
Write 6:35 pm in 24-hour time.
Worked solution
- 1
Identify the half of the day.
The hour is between 1 pm and 11 pm, so add 12.
- 2
Convert the hour.
A 24-hour clock continues counting after noon.
- 3
Keep the minutes.
Changing hour notation does not change the 35 minutes.
18:35
Just after midnight
Write 00:12 in 12-hour time.
Worked solution
- 1
Locate hour 00.
Hour 00 is the hour beginning at midnight.
- 2
Keep the 12 minutes past midnight.
The minutes remain 12, and midnight belongs to am.
12:12 am
Try it yourself.
Check your understanding
Write 12:45 pm in 24-hour time.
Show answer & reasoning
12:45
12:45 pm is 45 minutes after noon. Noon is 12:00 on a 24-hour clock, so the answer stays 12:45.
Keep practising
6 worksheet questions · 7 marks
Read the questions online
- Write 8:07 am in 24-hour time.1 mark
- Write 9:25 pm in 24-hour time.1 mark
- Write 12:10 am in 24-hour time.1 mark
- Write 17:42 in 12-hour time.1 mark
- Write 12:05 in 12-hour time.1 mark
- A student writes 7:50 pm as 07:50. Correct the time and explain.2 marks
Read the worked solutions
Equivalent correct methods earn the corresponding marks. Include units where asked.
- Write 8:07 am in 24-hour time.1 mark
Morning hour 8 remains 08; minutes stay 07.
08:07 - Write 9:25 pm in 24-hour time.1 mark
; retain 25 minutes.
21:25 - Write 12:10 am in 24-hour time.1 mark
The midnight hour is 00.
00:10 - Write 17:42 in 12-hour time.1 mark
; this is after noon.
5:42 pm - Write 12:05 in 12-hour time.1 mark
The 12 hour is noon, not midnight.
12:05 pm - A student writes 7:50 pm as 07:50. Correct the time and explain.2 marks
for the evening hour.
19:50. 07:50 is in the morning.
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum Mathematics
Converting 12-/24-hour time; elapsed time across midnight; timetables and journeys; time-zone differences; date changes; checking real-world scheduling answers.
Official curriculum source ↗