24 Hour Clock

We know that the units of time and their relationships. Now, we will learn to read a railway time table and a calendar.

Let us revise:

60 seconds = 1 minute

60 minutes = 1 hour

24 hours = 1 day

7 days = 1 week

52 weeks + 1 day = 1 year = 365 days

52 weeks + 2 days = 1 leap year = 366 days

10 years = 1 decade

100 years = 1 century

A year is divided into 12 months.

Note: In a leap year February has 29 days.

Reading Time from a Clock: Dial of the clock is divided into 60 evenly spaced divisions.

	Position of Hour Hand	Position of Minute Hand	Position of Time
	Between 2 and 3	At mark 38	2:38 (2 Hours 38 Minutes)
	Between 2 and 3	At mark 52	2:52 (2 Hours 52 Minutes)
	Between 2 and 3	At mark 23	2:23 (2 Hours 23 Minutes)

The 24-hour Clock Time:

In our daily life we use a 12-hour clock. But some departments like Railways, Airlines and Armed forces use 24-hour clock. Digital watches also show time in 24-hour clock time.

12-hour clock time                                24 hour clock time

12-midnight                                           2400 hours or 0000 hours

1 a.m.                                                   0100 hours

1:30 a.m.                                              0130 hours

4:50 a.m.                                              0450 hours

11.10 a.m.                                            1110 hours

12 noon                                                1200 hours

12:30 p.m.                                            1230 hours

1:00 p.m.                                              1300 hours

11:30 p.m.                                            2330 hours

In the 24-hour clock, the time from midnight to midnight is 1 day (24 hours)

Zero hours or 24 hours = midnight

12 hours = midday = noon                     12 hours = 1200 hours

2 p.m. = 1400 hours and so on               1 p.m. = 1300 hours

Note:

1. The numeral formed by the two digits from the right denotes the number of minutes.

2. If the numeral formed by the first two digits from the left is less than 12, it denotes the number of hours before noon and so a.m. is to be used with it.

3. If the numeral formed by the first two digits from the left is greater than 12, the difference between the number and 12 gives the number of hours after noon and so p.m. is to be used with it.

For example:

0845 hours                   08:45 a.m.

1020 hours                   10:20 a.m.

1345 hours                   01:45 p.m. (1345 – 1200 = 145)

2050 hours                   08:50 p.m. (2050 – 1200 = 850)

We normally use 12-hour clock system. The hour hand of the clock goes round the dial twice a day (24 hours). Some departments like railways, Airlines, etc use 24-hour clock system because they do not use a.m. and p.m. times.

In a 24-hour clock system, we express time in four digits. The first two digits represent hours and the last two digits represent the minutes.

On the dial there are two concentric circles. The inner circle has 1 to 12 numbers while the outer circle has 13 to 24 numbers.

In a 24-hour clock system, we start counting the time from midnight. Let us understand 24-hour system by considering some examples.  

(i) 12 midnight is denoted by 24 00 hours or 00 00 hour.

(ii) 12 noon is denoted by 12 00 hours.

(iii) 6 in the morning is denoted by 06 00 hours.

(iv) 10:25 in the evening is denoted by 22 25 hours. 
(10:25 + 12:00)

(v) 7:15 in the evening is denoted by 19 15 hours. 
(7:15 + 12:00)

From the above examples, we can conclude that between 12 midnight and 12 noon the 24-hour clock time is same.

For example, 10 40 hours = 10:40 a.m., 08 20 hours = 8:20 a.m., 11 30 hours = 11:30 a.m.

But between 12 noon and 12 midnight to convert the 24-hour clock time into 12-hour clock time, we subtract 12 from the 24-hour time.

For example, 19:30 hours = 19:30 – 12:00 = 7:30 p.m.

Similarly, to convert the 12-hour clock time into 24-hour clock time between 12 noon and 12 midnight, we add 12.

For example, 11:30 p.m. = 11:30 + 12:00 = 23:30 hours.

Therefore, the time which is shown by the inner circle is the time before noon and that shown by the outer circle is the time after noon.

These are some more examples:

After midnight          00:10 a.m. is shown as 00:10

                              02:45 a.m. is shown as 02:45

                              10:48 a.m. is shown as 10:48

                              02:45 p.m. is shown as 14:45

                              10:48 p.m. is shown as 22:48

               Clock                General Time                  24 hour clock

00:00 midnight (Just after midnight)  or,  12:00 midnight 06:00 a.m.(6 hours zero minutes in the morning) 12:00 noon

00:00 (Just after midnight) or, 24:00 hours 06:00 12:00

06:10 p.m.  08:30 p.m. 10:45 p.m.

18:10 20:30 22:45

We know how to use a.m. and p.m. to represent the time of the day in 12-hour clock. We know that a.m. is used to express time between 12 o’clock mid night to 12 o’clock noon and p.m. is used to express time between 12 o’clock noon to 12 o’clock midnight.

In 24-hour clock time, we express time in four digits. The first two digits from left represt hours and the last two digits represent the minutes.

So, to express time for a.m., we just write the time without separating hours and minutes.

For example 7:45 am is written as 0745 hours.

To express time for p.m. we add 12 to the hours and then write hours and minutes without separating them. For example 6:30 p.m. is written as (6 + 12), 1830 hours.

24-Hour Clock Time Format:

The hour hand of the clock goes round the clock twice a day that means 24 hours. 24-hour clock time does not have a.m. or p.m. In 24-hour clock system, we express time in four digits. The first two digits represent hours and the last two digits represent the minutes. There are no dots to separate hours and minutes. The time starts at 0000 hours or 2400 hours which is 12 midnight.

In a 24-hour clock system, we start counting the time from midnight. Let us understand 24-hour system by considering some examples.

1. Converting 12-Hour Clock to 24-Hour Clock Time Format:

12-Hour Time to 24-Hour Time Conversion Table

I. For the first hour of the day (12 Midnight to 12:59 a.m.), subtract 12 hours

For example:

(i) 12 Midnight = 0000 hours

(ii) 12:05 a.m. = 0005 hours

(iii) 12:40 a.m. = 0040 hours

II. From 1:00 a.m. to 12:59 p.m., no change.

For example:

(i) 6:40 a.m. = 0640 hours

(ii) 12:30 p.m. = 1230 hours

(iii) 10:45 a.m. = 1045 hours

III. From 1:00 p.m. to 11:59 p.m., add 12 hours

(i) 3:45 p.m. = 1545 hours (3:45 + 12)

(ii) 6:20 p.m. = 1820 hours (6:20 + 12)

(iii) 08:55 p.m. = 2055 hours (8:55 + 12)

2. Converting 24-Hour Clock to a.m. or p.m.

I. For the first hour of the day (0000 to 0059), add 12 hours to make it a.m.

For example:

(i) 0001 hours = 12:01 a.m.

(ii) 0048 hours = 12:48 a.m.

II. From 0100 hours to 1159 hours, just add a.m. after the hours.

For example:

(i) 0225 hours = 2:25 a.m.

(ii) 1150 hours = 11:50 a.m.

III. From 1200 hours to 12 hours 59, just add p.m. after the hours.

For example:

(i) 1235 hours = 12:35 p.m.

(ii) 1205 hours = 12:05 p.m.

IV. From 1300 hours to 23 hours 59, subtract 12 hours to make it p.m.

For example:

(i) 1355 hours = 1:55 p.m.

(ii) 1725 hours = 5:25 p.m.

Questions and Answers on 24 Hour Clock Time Format:

I. Convert the time given in a.m. and p.m. form into the 24-hour form. One is shown as an example.

(i) 1 : 24 p.m.

1 : 24 p.m. = 1 : 24 + 12 : 00

                    = 13 : 24

1 : 24 p.m. = 1324 hours

(ii) 7 : 16 a.m.

(iii) 4 : 55 a.m.

(iv) 6 : 54 p.m.

(v) 9 : 33 p.m.

(vi) 11 : 42 p.m.

Answers:

I. (ii) 0716 hours

(iii) 0455 hours

(iv) 1854 hours

(v) 2133 hours

(vi) 2342 hours

II. Convert the time given in 24- hour form into a.m./p.m. form. One is shown as an example.

(i) 1341 hours

1341 = 1341 – 1200

        = 1 : 41 p.m.

1341 = 1 : 41 p.m.

(ii) 2325 hours

(iii) 1750 hours

(iv) 0853 hours

(v) 0432 hours

(vi) 1539 hours

Answers:

II. (ii) 11 : 25 p.m.

(iii) 05 : 50 p.m.

(iv) 08 : 53 a.m.

(v) 04 : 32 a.m.

(vi) 03 : 39 p.m.

III. Convert the following 12-hour clock time to 24-hour clock time.

(i) 7:15 p.m.

(ii) 6:45 a.m.

(iii) 12:15 p.m.

(iv) 2:50 a.m.

(v) 10:10 p.m.

(vi) 6:30 p.m.

Answer:

III. (i) 1915 hours

(ii) 0645 hours

(iii) 1215 hours

(iv) 0250 hours

(v) 2210 hours

(vi) 1830 hours

IV. Change to 24 hour clock time:

(i) 4:15 a.m.

(ii) 6:30 p.m.

(iii) 12:45 p.m.

(iv) 1:20 a.m.

(v) 9:30 a.m.

(vi) 10:25 p.m.

Answer:

IV. (i) 0415 hours

(ii) 1830 hours

(iii) 1245 hours

(iv) 0120 hours

(v) 0930 hours

(vi) 2225 hours

V. Convert the following 24-hour clock time to 12-hour clock time.

(i) 1345 hours

(ii) 0330 hours

(iii) 2035 hours

(iv) 0515 hours

(v) 1655 hours

(vi) 1945 hours

Answer:

V. (i) 1:45 p.m.

(ii) 3:30 a.m.

(iii) 8:35 p.m.

(iv) 5:15 a.m.

(v) 4:55 p.m.

(vi) 7:45 p.m.

VI. Change to 12 hour clock time:

(i) 1700 hours

(ii) 1535 hours

(iii) 0030 hours

(iv) 2000 hours

(v) 2215 hours

(vi) 2300 hours

Answer:

VI. (i) 5:00 p.m.

(ii) 3:35 p.m.

(iii) 12:30 a.m.

(iv) 8:00 p.m.

(v) 10:15 p.m.

(vi) 11 p.m.

VII. Write the correct 24-hour clock time with each analog clock.

Answers:

VII. (i) 1535 hours

(ii) 0505 hours

(iii) 2015 hours

(iv) 0400 hours

(v) 0150 hours

(vi) 2020 hours

(vii) 2230 hours

(viii) 1955 hours

VIII. The train, Charminar Express runs between Hyderabad and Chennai. The arrival and departure time of it at different stations are given below.

a → Arrival Time

d → Departure Time

Observe the table and answer the following questions in 12-hour clock time.

(i) When does the train arrive at Warangal station?

(ii) At what time does the train leave Vijayawada station?

(iii) When does the train start from Hyderabad station?

(iv) At what time does the train reach Chennai?

Answer:

VIII. (i) 9:59 p.m.

(ii) 1:55 a.m.

(iii) 7:00 p.m.

(iv) 9:20 a.m.

Related Concepts

● Units for Measuring Length

● Measuring Instruments

● To Measure the Length of a Line-segment

● Perimeter of a Figure

● Unit of Mass or Weight

● Examples on Unit of Mass or Weight

● Units for The Measurement of Capacity

● Examples on Measurement of Capacity

● Measurement of Time

● Read a Watch or a Clock

● Antemeridian (a.m.) or Postmeridian (p.m.)

● What Time it is?

● Time in Hours and Minutes

● 24 Hour Clock

● Units of Time

● Examples Units of Time

● Time Duration

● Calendar

● Reading and Interpreting a Calendar

● Calendar Guides us to Know

4th Grade Math Activities

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