ClockHubClockHubtwenty-one hundred
Military time writes every hour of the day as a two-digit number from 00 to 23, then appends the minutes as two more digits. 2100 therefore means 21 hours and 00 minutes past midnight — 9:00 PM on a 12-hour clock.
Read aloud it becomes "twenty-one hundred". A zero minutes value is spoken as "hundred", which is why whole hours end in "hundred"; minutes below ten take an "oh" in front, as in "seventeen oh five" for 1705.
Twelve-hour clocks split the day at noon. Hours 00 through 11 are AM, hours 12 through 23 are PM, and the two boundary hours are the ones people get wrong: 0000 is 12:00 AM and 1200 is 12:00 PM. 2100 sits on the PM side of that line, which is why it converts to 9:00 PM.
Going the other way is the same arithmetic in reverse. Take 9 and PM, drop the suffix, and add 12 to any PM hour — then watch the two twelve-o’clock cases, where 12 AM becomes 00 and 12 PM stays 12. 9:00 PM becomes 2100.
| Military | Standard | Spoken |
|---|---|---|
| 2000 | 8:00 PM | twenty hundred |
| 2015 | 8:15 PM | twenty fifteen |
| 2030 | 8:30 PM | twenty thirty |
| 2045 | 8:45 PM | twenty forty-five |
| 2100 | 9:00 PM | twenty-one hundred |
| 2110 | 9:10 PM | twenty-one ten |
| 2115 | 9:15 PM | twenty-one fifteen |
| 2120 | 9:20 PM | twenty-one twenty |
| 2130 | 9:30 PM | twenty-one thirty |
| 2140 | 9:40 PM | twenty-one forty |
| 2145 | 9:45 PM | twenty-one forty-five |
| 2200 | 10:00 PM | twenty-two hundred |