Understand the idea.
From 12-hour to 24-hour time
When converting to 24-hour time, keep morning hours 1 to 11 and write two hour digits. For pm hours 1 to 11, add 12. Keep the minute digits exactly as they are.
Treat hour 12 separately: 12 am becomes 00, while 12 pm stays 12. Thus 12:15 am becomes 00:15. The label changes which half of the day the hour belongs to.
From 24-hour to 12-hour time
When converting back, hours 13 to 23 need 12 subtracted and a pm label. Hours 01 to 11 keep their number and use am. Minutes still stay unchanged.
Hour 00 is written as 12 am; hour 12 is written as 12 pm. Check that the answer fits the same part of the day, especially near noon or midnight.
See the method in action.
Convert an afternoon time
Write 5:45 pm in 24-hour time.
Worked solution
- 1
Convert the afternoon hour.
The given pm hour is between 1 and 11, so it lies twelve hours after its morning partner.
- 2
Keep the minutes and write the time.
Only the hour field changes; the 45-minute part stays the same.
- 3
Check the reverse conversion.
Hour 17 returns to hour 5 pm, confirming the afternoon time.
17:45
Convert a time after midnight
Write 00:20 in 12-hour time.
Worked solution
- 1
Identify hour 00.
Hour 00 is the hour immediately after midnight, which is labelled 12 am on a 12-hour clock.
- 2
Keep the twenty-minute part.
The minute field still records twenty minutes after the hour.
- 3
Check the part of the day.
The am label places the time just after midnight rather than just after noon.
12:20 am
Try it yourself.
Check your understanding
Convert 18:08 to 12-hour time.
Show answer & reasoning
6:08 pm
Hour 18 is after noon. Subtract , retain minutes 08 and add pm: 6:08 pm.
Keep practising
6 worksheet questions · 7 marks
Read the questions online
- Convert 7:09 am to 24-hour time.1 mark
- Convert 2:36 pm to 24-hour time.1 mark
- Convert 12:05 pm to 24-hour time.1 mark
- Convert 12:05 am to 24-hour time.1 mark
- Convert 23:50 to 12-hour time.1 mark
- Mia writes 6:15 pm as 06:15. Correct the time and explain the error.2 marks
Read the worked solutions
Equivalent correct methods earn the corresponding marks. Include units where asked.
- Convert 7:09 am to 24-hour time.1 mark
Keep morning hour 7; write it with two digits.
07:09 - Convert 2:36 pm to 24-hour time.1 mark
; keep 36 minutes.
14:36 - Convert 12:05 pm to 24-hour time.1 mark
The hour after noon stays 12.
12:05 - Convert 12:05 am to 24-hour time.1 mark
The hour after midnight is 00.
00:05 - Convert 23:50 to 12-hour time.1 mark
; this is before midnight, so pm.
11:50 pm - Mia writes 6:15 pm as 06:15. Correct the time and explain the error.2 marks
for an evening hour.
18:15; 06:15 means 6:15 am.
Curriculum reference & lesson scope
Australian Curriculum v9 / SA Curriculum Mathematics 2026
12-/24-hour clocks; conversion; interpreting schedules.
Official curriculum source ↗