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21:00 in 12-Hour Time
21:00 is 9:00 PM.
Written 2100 in military time and said “twenty-one hundred hours”. Going the other way, 9:00 PM is 21:00.
The 21:00 hour is late evening: last trains, closing times and the end of most opening hours.
24-hour clock
21:00
12-hour clock
9:00 PM
Said aloud: “twenty-one hundred hours” on the 24-hour clock, “nine o'clock at night” on the 12-hour one.
Why 21:00 converts the way it does
This is the half of the day that actually changes. From 13:00 to 23:00, subtract 12 to get the 12-hour hour and label it PM: 21 − 12 = 9, so 21:xx is 9:xx PM. Going the other way, add 12 to any PM hour except 12 PM itself.
The minutes are the same on both clocks — a whole hour stays a whole hour — and 21:00 is at night, which is the information the AM/PM label is carrying.
Need this time to actually do something? Set an alarm for 9:00 PM, or use the timer to count a length of time instead of waiting for a clock time.
Common questions
What is 21:00 in 12-hour time?
21:00 is 9:00 PM. The minutes are unchanged; the hour is 21 − 12 = 9, and it takes PM.
What is 9:00 PM in 24-hour time?
9:00 PM is 21:00, written 2100 in military time.
How do you say 2100 out loud?
In military time it is said "twenty-one hundred hours". On a 12-hour clock the same moment is "nine o'clock at night".