Understanding Time Formats: 12-Hour vs. 24-Hour

Time keeping around the world relies primarily on two major formatting systems: the 12-hour clock and the 24-hour clock. Understanding how these differ, and how to seamlessly convert between them, is essential for global coordination.

The 12-Hour Format (AM/PM)

The 12-hour clock splits the day into two distinct halves. The first 12 hours run from midnight to noon, and the second 12 hours run from noon to midnight.

AM (Ante Meridiem): Meaning "before midday," this covers the period from 12:00 Midnight up to 11:59 in the morning.
PM (Post Meridiem): Meaning "after midday," this covers the period from 12:00 Noon up to 11:59 at night.

Pro Tip: 12:00 AM can be confusing! A good trick to remember is that the "P" in PM stands for "Post" (after) noon. Therefore, 12:00 PM is exactly noon, and 12:00 AM is the moment a new day begins at midnight.

The 24-Hour Format

Also known as "military time" in North America or standard time in much of the rest of the world, the 24-hour format runs continuously from 00:00 (midnight) to 23:59.

Using this standard eliminates the ambiguity of AM/PM entirely. It is highly recommended for international scheduling, transport timetables, and technical applications.

24:00 vs 00:00: While both correspond to midnight, 24:00 is occasionally used to explicitly denote the exact end of a day or a time range (e.g., "Open from 16:00 to 24:00"), whereas 00:00 denotes the start of the day.
Military Usage: In strict military contexts, the colon is often omitted, resulting in formats like "0430" (spoken as "zero four thirty").

Converting Between the Two

Converting back and forth is straightforward once you know the rules.

12-Hour to 24-Hour

For times in the AM: Leave the hour unchanged (just add a leading zero if it's less than 10). The special exception is 12:XX AM, which translates to 00:XX.
For times in the PM: Add 12 to the hour. For example, 4:00 PM becomes 16:00. The exception is 12:XX PM, which remains 12:XX.

24-Hour to 12-Hour

00:00 - 11:59: The time remains the same, but you append "AM" at the end. (00:00 becomes 12:00 AM).
12:00 - 23:59: Subtract 12 from the hour (except for 12:XX) and append "PM". For example, 19:30 becomes 7:30 PM.

Precision in Time

Depending on your needs, time formatting can get incredibly precise. When tracking exact logistical timelines, seconds are appended after an additional colon (16:30:56), and milliseconds can be added following a decimal point (16:30:56.836).