Primary 5 Foundation maths · Measurement & time · About 12 minutes
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
- 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
The short and long hands have different jobs. A new notation can describe the same instant, with the day period made clear.
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 4:09 pm 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.
Afternoon time Determine whether it is before or after noon.
Afternoon time Write 4:09 pm in 24-hour time.
16:09
Decide whether it is before or after noon.
Afternoon time Add 12 to 4, giving 16.
Afternoon time Write the minutes unchanged: 16:09.
Afternoon time Check the result against the question we started with.
16:09 represents the same hour and minute in the stated half of the day.
We found 16:09. The 24-hour clock counts hours from midnight. Change the hour notation when needed, but keep the minutes the same.
Afternoon 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
- 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.
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