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12/24 hr clock conversion table, how clocks work

24-hour/12-hour time conversion
24-hour 12-hour
0h 01-0h 59 12:01am-12:59am
1h 00 1:00am
2h 00 2:00am
3h 00 3:00am
4h 00 4:00am
5h 00 5:00am
6h 00 6:00am
7h 00 7:00am
8h 00 8:00am
9h 00 9:00am
10h 00 10:00am
11h 00 11:00am
12h 00-12h 59 12:00pm-12:59pm (noon)
13h 00 1:00pm
14h 00 2:00pm
15h 00 3:00pm
16h 00 4:00pm
17h 00 5:00pm
18h 00 6:00pm
19h 00 7:00pm
20h 00 8:00pm
21h 00 9:00pm
22h 00 10:00pm
23h 00 11:00pm
24h 00 12:00am (midnight)

clocks in general

Clocks in general have 12 or 24 hours, 60 minutes in every hour, and 60 seconds in every minute.

Seconds can be broken down into smaller parts such as milliseconds, microseconds picoseconds, and nanoseconds, but there really is no standard in use except the NIST (National Institute of Standards and Technology) Atomic Clock and this varies with the need, and the NIST clock is not available to everyone. most web browsers's javascript uses milliseconds. PC's use a different time standard that needs to be updated periodically because it gets out of sync with the real time. This is why PC's Operating Systems from XP and and up have "Internet Time" (NNTP).

12-hour time

in a 12 hour clock there are really 24 hours, 12 hours from midnight to noon and 12 hours from noon to midnight.

to convert 12-hour time to 24-hour time, you need to do 2 things:

  • for the range of 1pm to 12am, add 12 to the hour.
  • for the range of 12am to the the time just before 1am (12:59:59am), subtract 12 from the hour.

24-hour time

In a 24-hour clock there are still 24 hours,

The time immediately after 24h 00 is 0h 01 through 0h 59. 24h and 0h converts to 12:00am, because 24h and 0h are the same position on a 24hour clock. The time from 12h 00 through 12h 59 converts to 12:00pm through 12:59pm.

To convert 24-hour time in the 13h to 24h range, subtract 12 from the hour.