Primary 3 maths · Measurement & time · About 10 minutes
Read and use the 24-hour clock
Read the hour and minute roles separately, then use the morning or afternoon information.
Start the interactive lesson →Open practice activity
What you will learn
- Read and use the 24-hour clock
Models used: number sentences, stories, diagrams.
Before you start
Name the hour without am or pm
A clock shows 9 o’clock in the evening. How do we write that time using the 24-hour clock?
In the morning, nine o’clock is written 09:00. The two digits after the colon count minutes.
09:00
9:00 am = 09:00 After noon, keep counting the hours beyond twelve. Nine in the evening is twelve plus nine: 21.
12 + 9 = 21; 9:00 pm = 21:00
9:00 pm = 21:00 The minutes do not change. A quarter past nine in the evening is 21:15.
9:15 pm = 21:15
9:15 pm = 21:15 Hours since the start of the day. Read each value with the heading above its column.
Remember the two boundary times: midnight begins the day at 00:00; noon is 12:00.
Hours since the start of the day Time of day 24-hour time Midnight 00:00 Noon 12:00 9 pm 21:00
What did the picture help us see?
Remember the two boundary times: midnight begins the day at 00:00; noon is 12:00.
Worked example: A new example, together
Write 1:06 am in 24-hour time.
Read the hour and minute roles separately, then use the morning or afternoon information.
The 24-hour clock counts hours from midnight. Change the hour notation when needed, but keep the minutes the same.
Morning time Determine whether it is before or after noon.
Morning time Write 1:06 am in 24-hour time.
01:06
Keep the morning hour 1, with a leading zero if needed.
Morning time Write the minutes unchanged: 01:06.
Morning time Check the result against the question we started with.
01:06 represents the same hour and minute in the stated half of the day.
We found 01:06. The 24-hour clock counts hours from midnight. Change the hour notation when needed, but keep the minutes the same.
Morning time
Common mistakes to discuss
- Adding twelve to every time. Only afternoon and evening hours change. 9:15 am is 09:15, while 4:09 pm is 16:09.
Check your understanding
- Read and use the 24-hour clock
- connect clock hands and time notation without changing the instant
- check the answer against the original quantities and units
Explain your reasoning to an adult, then try a fresh question in the interactive lesson. A result from one attempt is not proof of lasting mastery.
Try this lesson →Related Primary 3 lessons
- Add and subtract money in decimal notationAdd and subtract money in decimal notation · About 10 minutes
- Measure length in kilometres and liquid volume in millilitresMeasure length in kilometres and liquid volume in millilitres · About 10 minutes
- Use compound measurement unitsUse compound measurement units · About 10 minutes
- Convert km and m; m and cm; kg and g; litres and mlConvert km and m; m and cm; kg and g; litres and ml · About 10 minutes
- Use seconds as a unit of timeUse seconds as a unit of time · About 10 minutes
- Find start times, finish times and durationsFind start times, finish times and durations · About 10 minutes