The idea, step by step
From 12-hour to 24-hour time
For 1:00 am to 11:59 am, keep the hour and use two digits if needed: 6:07 am becomes 06:07. For 1:00 pm to 11:59 pm, add 12 to the hour: 4:25 pm becomes 16:25. Minutes do not change.
The two special cases use the number 12: noon stays 12:00; midnight becomes 00:00. Times just after midnight, such as 12:15 am, become 00:15.
From 24-hour to 12-hour time
Hours 13 to 23 are afternoon or evening. Subtract 12 from the hour and add pm. Thus 21:40 becomes 9:40 pm. Hours 01 to 11 use am.
An hour field of 00 becomes 12 am; an hour field of 12 becomes 12 pm. Check the story: a 15:00 school finish belongs in the afternoon, not the early morning.
A common trap
Add 12 to every pm time, including 12:30 pm.
Instead: Noon is already hour 12. Only pm hours 1 to 11 need another 12 added.
See the thinking
Convert an afternoon time
Write 5:45 pm in 24-hour time.
- For a pm hour from 1 to 11, add 12: 5 + 12 = 17.
- Keep 45 minutes.
Convert a time after midnight
Write 00:20 in 12-hour time.
- The hour 00 is the first hour of the day, after midnight.
- Use 12 as the 12-hour number and add am.
Check your understanding
Convert 18:08 to 12-hour time.
Show answer
6:08 pm
18 − 12 = 6; the minutes remain 08.
Your turn
6 questions · 7 marks · Work at your own pace.
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
2 + 12 = 14; 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
23 − 12 = 11; 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
6 + 12 = 18 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 ↗