Compare 12- and 24-hour time systems and convert between them (ACMMG110)

LO: To compare and convert 12- and 24-hour time notation.


  • that the concepts of time (hours, minutes, days)

  • how to read a clock using the clock hands (small hand = hour, large hand = minute)

  • ante meridiem = am = before midday

  • post meridiem = pm = after midday

  • 1:00 pm = 1 hour after midday (13th hour of the day) = 1300

  • common language such as ‘quarter to’, ‘quarter past’ and ‘half past’ to describe time.


  • that time can be represented in 12- and 24 hours time periods.

  • time is a measurement that relies on the base 60 number system. There are 60 seconds in a minute and 60 minutes in an hour.


  • I compare and convert using 12- and 24-hour time notation.

AM and PM are representations of time.

AM means ante meridiem which means before noon.
PM means post meridiem which means after noon.
So any time period that occurs before noon (12:00 midday) is in AM time.
Any time period that occurs after noon (12:00 midday) is in PM time.

We can also use 12- or 24-hour time to represent time. 24-hour time is also called military time.

24-hour time notation is basically just carrying on the time from the AM. Instead of going back to 1 o’clock and swapping it over to PM, it continues on to 13:00 all the way up to 23:59.

If the time is in AM, it’s easy to convert to 24-hour time because all you need to do is take away the AM and write it as is. Eg.) 8:00 am is 8:00

If the time is in PM, all you need to do is add 12 hours to your original time, because it is after midday. Eg.) 8:00 PM is 8:00 + 12:00 which is 20:00.


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