Converting Between 12-Hour and 24-Hour Clock — Quick Guide

24 Hour Clock: How It Works and Why It’s Useful

What it is

The 24-hour clock (also called military time or astronomical time) numbers the hours of the day from 00 to 23. Midnight is 00:00, noon is 12:00, and the day ends at 23:59 before rolling back to 00:00.

How it works

• Hour format: Hours run 00–23 instead of repeating 1–12 twice.
• Minutes/seconds: Written after a colon, e.g., 14:30 = 2:30 PM, 00:15 = 12:15 AM.
• Conversion rules:
  1. For times from 00:00–00:59, keep the hour as 00 (midnight hour).
  2. For 01:00–11:59, the time is the same as AM in 12-hour format.
  3. For 12:00–12:59, keep as 12 (noon hour).
  4. For 1:00 PM–11:59 PM, add 12 to the hour (e.g., 1:00 PM → 13:00, 11:45 PM → 23:45).

Why it’s useful

• Eliminates ambiguity: No need for AM/PM labels; 08:00 and 20:00 are distinct.
• Simplifies scheduling: Easier for timetables, transportation, healthcare, and shift work.
• Better for computing: Straightforward for time arithmetic and sorting since times increase monotonically through the day.
• Global standardization: Widely used internationally and in technical contexts, reducing cross-cultural confusion.

Quick reference

• Midnight: 00:00
• 6:30 AM: 06:30
• Noon: 12:00
• 7:45 PM: 19:45

Tip for switching

• Practice by reading schedules and converting common times (e.g., morning commute, lunch, evening events) until it becomes intuitive.