12-hour and 24-hour time
Read, write, and convert time between analogue and digital 12-hour and 24-hour clocks
What a learner can do afterwards
- Convert 3:45 pm to 15:45 in 24-hour time
- Read 19:30 and state the 12-hour equivalent as 7:30 pm
- Match a set of 12-hour and 24-hour times
The lesson
You have used clocks that count 1 to 12, with am for morning and pm for afternoon or evening. There is another way to write time called the 24-hour clock. It counts hours from 00 all the way to 23, so you never need am or pm.
To change an afternoon or evening time into 24-hour time, add 12 to the hour. So 3:45 pm becomes 3 + 12 = 15, which is 15:45. Morning hours before noon stay almost the same. You just add a zero in front if the hour is a single digit, so 9:15 am becomes 09:15.
A train leaves at 19:30. To find the 12-hour time, subtract 12 from the hour: 19 - 12 = 7. So the train leaves at 7:30 pm, in the evening.
Watch out for two special times. Noon is 12:00 pm, and midnight is 00:00 in the 24-hour clock. Neither one follows the usual add-12 or subtract-12 rule.
24-hour time skips am and pm: add 12 to afternoon and evening hours, and keep morning hours almost the same.
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Where it sits
Learn first
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Where this leads
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.