AM* and PM* Abbreviation(s), Latin phrase, Meaning
Abbreviation(s) Latin phrase Meaning
AM
A.M.
am
a.m.
Ante Meridiem
Ante Meridian
Latin = "before midday"
before noon
PM
P.M.
pm
p.m.
Post Meridiem
Post Meridian
Latin = "after midday"
after noon
Afternoon
*
  • Terms 12 a.m. and 12 p.m. cause confusion and should not be used as neither the "12 am" nor the "12 pm" designation is technically correct.
  • It advisable to use 12 noon and 12 midnight where clarity is required.
  • To avoid ambiguity, airlines, railroads, and insurance companies use 12:01am for an event beginning the day, 11:59pm for ending it.
Converting from AM / PM to 24 hour clock
12 midnight to 12:59 AM 1:00 AM to 12:59 PM
1:00 PM to 11:59 PM
subtract 12 hours straight conversion
add 12 hours:
EXAMPLES:
12 midnight --> 0000
12:13 AM --> 0013
12:59 AM --> 0059
EXAMPLES:
01:00 AM --> 0100
08:00 AM --> 0800
11:59 AM --> 1159
12 noon --> 1200
12:01 PM --> 1201
12:45 PM --> 1245
12:59 PM --> 1259
EXAMPLES:
01:00 PM --> 1300
03:30 PM --> 1530
06:00 PM --> 1800
09:00 PM --> 2100
10:30 PM --> 2230
11:05 PM --> 2305
11:59 PM --> 2359


Converting from 24 hour clock to AM / PM
0000 to 0059 0100 to 1159
1200 to 1259 1300 to 2359
add 12 hours straight conversion to AM
straight conversion to PM subtract 12 hours
EXAMPLES:
0000 --> 12 midnight
0015 --> 12:15 AM
0030 --> 12:30 AM
0059 --> 12:59 AM
EXAMPLES:
0100 --> 01:00 AM
0300 --> 03:00 AM
0700 --> 07:00 AM
0830 --> 08:30 AM
1000 --> 10:00 AM
1159 --> 11:59 AM
EXAMPLES:
1200 --> 12 noon
1215 --> 12:15 PM
1230 --> 12:30 PM
1259 --> 12:59 PM
EXAMPLES:
1300 --> 01:00 PM
1500 --> 03:00 PM
1800 --> 06:00 PM
2030 --> 08:30 PM
2215 --> 10:15 PM
2359 --> 11:59 PM

Note: Read BC and AD and BCE Meaning. Christian calendar concepts.









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