There are 24 hours in a day. The first 12 of them are called "am" (from the Latin ante meridiem, meaning "before midday"), the last 12 are called "pm" (from the Latin post meridiem, "after midday").
Of cause if you use a 24 hour clock the terms "am" and "pm" are not needed.
12 Hours ! There are 12 hours in the AM and 12 hours in the PM !
12 hours
12 hours
From midnight (am) to Noon (pm) is 12 hours.
2.5 hours
2 hours
3 hours
7 and a half hours
21 hours
2 hours.
6 hours.
There are 16 hours from 4 am to 8 pm. 4 am to 4 pm is 12 hours, then 4 pm to 8 pm is another 4 hours.