24-Hour Clock
The 12-hour clock uses AM and PM to tell apart morning and evening times. The 24-hour clock avoids this confusion by numbering hours from 00:00 (midnight) to 23:59.
In Class 4, you will learn to read, write, and convert between 12-hour and 24-hour time.
What is 24-Hour Clock - Class 4 Maths (Time)?
The 24-hour clock (also called railway time or military time) counts hours from 0 to 23:
- 00:00 = midnight (12:00 AM)
- 12:00 = noon (12:00 PM)
- 13:00 = 1:00 PM
- 23:59 = 11:59 PM (one minute before midnight)
The format is always HH:MM — two digits for hours and two digits for minutes.
24-Hour Clock Formula
12-hour → 24-hour (PM times): Add 12 to the hour
24-hour → 12-hour (after 12:59): Subtract 12 from the hour, add PM
AM times (except 12 AM): Same number, just write two digits. 9:00 AM = 09:00.
12:00 AM (midnight) = 00:00. 12:00 PM (noon) = 12:00.
Types and Properties
Conversion table:
| 12-Hour | 24-Hour |
|---|---|
| 12:00 AM (midnight) | 00:00 |
| 1:00 AM | 01:00 |
| 6:00 AM | 06:00 |
| 11:00 AM | 11:00 |
| 12:00 PM (noon) | 12:00 |
| 1:00 PM | 13:00 |
| 3:30 PM | 15:30 |
| 6:45 PM | 18:45 |
| 9:00 PM | 21:00 |
| 11:59 PM | 23:59 |
Solved Examples
Example 1: Example 1: PM to 24-hour
Problem: Convert 4:30 PM to 24-hour format.
Solution:
Step 1: It is PM (afternoon), so add 12 to the hour.
Step 2: 4 + 12 = 16. Minutes stay the same.
Answer: 4:30 PM = 16:30.
Example 2: Example 2: AM to 24-hour
Problem: Convert 7:15 AM to 24-hour format.
Solution:
Step 1: AM times before noon stay the same.
Step 2: Write with two digits: 07:15.
Answer: 7:15 AM = 07:15.
Example 3: Example 3: 24-hour to 12-hour (afternoon)
Problem: Convert 19:45 to 12-hour format.
Solution:
Step 1: 19 > 12, so subtract 12. 19 − 12 = 7.
Step 2: Since the original hour was 13 or more, it is PM.
Answer: 19:45 = 7:45 PM.
Example 4: Example 4: Midnight
Problem: What is 12:00 AM in 24-hour format?
Solution:
Step 1: 12:00 AM (midnight) is the start of a new day.
Step 2: In 24-hour format, midnight = 00:00.
Answer: 12:00 AM = 00:00.
Example 5: Example 5: Noon
Problem: What is 12:30 PM in 24-hour format?
Solution:
Step 1: 12 PM stays as 12 in 24-hour format (do NOT add 12).
Answer: 12:30 PM = 12:30.
Example 6: Example 6: Train timetable
Problem: A train departs at 14:20 and arrives at 18:05. How long is the journey?
Solution:
Step 1: 18:05 − 14:20.
Step 2: Hours: 18 − 14 = 4. Minutes: 05 − 20 → borrow 1 hour.
Step 3: 17:65 − 14:20 = 3 hours 45 minutes.
Answer: The journey takes 3 hours 45 minutes.
Example 7: Example 7: Converting a schedule
Problem: Priya's schedule shows: Maths at 09:00, Lunch at 12:30, Sports at 15:00. Convert to 12-hour format.
Solution:
Step 1: 09:00 → 9:00 AM.
Step 2: 12:30 → 12:30 PM.
Step 3: 15:00 → 15 − 12 = 3:00 PM.
Answer: Maths at 9:00 AM, Lunch at 12:30 PM, Sports at 3:00 PM.
Example 8: Example 8: Night time
Problem: Aman goes to bed at 21:30 and wakes up at 06:00. How long does he sleep?
Solution:
Step 1: 21:30 to 00:00 (midnight) = 2 hours 30 minutes.
Step 2: 00:00 to 06:00 = 6 hours.
Step 3: Total = 8 hours 30 minutes.
Answer: Aman sleeps for 8 hours 30 minutes.
Example 9: Example 9: Late night event
Problem: Convert 11:45 PM to 24-hour format.
Solution:
Step 1: 11 + 12 = 23.
Answer: 11:45 PM = 23:45.
Key Points to Remember
- The 24-hour clock runs from 00:00 (midnight) to 23:59.
- AM times (1-11 AM) → same hour in 24-hour format (e.g., 9 AM = 09:00).
- 12:00 AM (midnight) = 00:00.
- 12:00 PM (noon) = 12:00 (do not add 12).
- PM times (1-11 PM) → add 12 to the hour (e.g., 3 PM = 15:00).
- 24-hour times above 12 → subtract 12 and add PM (e.g., 20:00 = 8 PM).
- Used in railways, airports, military, and many countries.
Practice Problems
- Convert 5:45 PM to 24-hour format.
- Convert 22:10 to 12-hour format.
- What is 12:00 AM in 24-hour time?
- A flight departs at 16:40 and arrives at 20:15. How long is the flight?
- Convert these to 24-hour: 8:00 AM, 12:00 PM, 6:30 PM, 11:00 PM.
- A train arrives at 01:30. Is this AM or PM? How do you know?
- Arrange in order from earliest to latest: 15:00, 09:30, 23:00, 06:45, 12:15.
Frequently Asked Questions
Q1. What is the 24-hour clock?
The 24-hour clock counts hours from 00 (midnight) to 23 (11 PM). It eliminates the need for AM and PM. For example, 3 PM is written as 15:00.
Q2. How do you convert PM to 24-hour time?
Add 12 to the hour. 5:30 PM → 5 + 12 = 17 → 17:30. Exception: 12 PM stays as 12:00 (do not add 12).
Q3. How do you convert 24-hour time to 12-hour?
If the hour is 13 or more, subtract 12 and add PM. If the hour is 1-11, keep it and add AM. 00:xx is 12:xx AM.
Q4. Why is 12 AM written as 00:00?
Midnight marks the start of a new day, so the hour resets to 0. In 24-hour format, midnight = 00:00, and the day counts up from there.
Q5. Why do trains and airports use 24-hour time?
It avoids confusion between AM and PM. A flight at 02:00 is clearly 2 AM, while 14:00 is clearly 2 PM. This prevents passengers from mixing up morning and afternoon times.
Q6. Is 24:00 the same as 00:00?
24:00 of one day is the same moment as 00:00 of the next day. Most systems use 00:00 for midnight.
Q7. How do you calculate duration using 24-hour time?
Subtract the departure time from the arrival time. If minutes require borrowing, borrow 1 hour (= 60 minutes). Example: 18:10 − 14:45 = 17:70 − 14:45 = 3 hours 25 minutes.
Q8. What is another name for the 24-hour clock?
It is also called military time (used by armies), continental time, or railway time (used by Indian Railways).
