# 12 hour clock 24 hour clock

```TIME
12 hour clock
For the 12 hour clock, the important time is 12 noon, which is the meridian. Time is
measured in two 12 hour cycles, which are either the 12 hours before 12 noon, which are
am, or the 12 hours after 12 noon which are pm.
 am stands for ante meridian which means before 12 noon
 pm stands for post meridian which means after 12 noon
 2am
5.45pm
12 noon
12 midnight
24 hour clock
In the 24 hour clock, time is measured in one 24 hour cycle, starting from immediately after
midnight.
 When the time is on the precise hour it is given in hundreds.
 0200 hours is read as &quot;oh two hundred hours&quot;
 1200 hours is read as &quot;twelve hundred hours&quot;
 2400 hours is read as &quot; twenty four hundred hours&quot;
 When minutes are involved the number for the hours is given first, followed by the
minute time.
 1745 hours is read as &quot;seventeen forty-five hours&quot;
 0312 hours is read as &quot;oh three twelve hours&quot;
Comparative times
Noon
Midnight
12.01am
1.00am
12.00noon
12.01pm
12.00pm
0001hours
0100hours
1200hours
1201hours
2400hours
1
Updated Feb 2013
Converting between time systems
Given the time on a 12 hour clock you need to be able to convert it for a 24 hour clock.
 For the hours between 1 and 12, just write them down, with a 0 in front of a single digit
number, followed by the minutes.
 1.32am

0132hours
 11.45am

1145hours
 For the hour between midnight (12.00pm) and 1am, you need to write 00 for the hour,
followed by the minute time.
 12.17am

0017hours
 For the hours between 12 noon and midnight (12.00pm) you need to add on 12 hours to
the given time, then convert as before.
 3.30pm

1530hours
 11.55pm

2355hours
You also need to be able to convert from a 24 hour clock to a 12 hour clock.
 For the hours between 1 and 12, just write the hours down, without the 0 in front for
the single digit numbers, followed by a point, then the minutes.
 0525hours

5.25am
 1057hours

10.57am
 For the hour between midnight (12.00pm) and 1am, you need to replace the 00 with 12.
 0050hours

12.50am
 For the hours between 1200 hours (12 noon) and 2400 hours
midnight), you need to subtract 1200, then convert as before.
 1812hours

6.12pm
 1235hours

12.35pm
2
Updated Feb 2013
(12
Time problems
 How many minutes from 7.30am to 12.45am?
7.30am to 12.00am (12 noon)
= 4 hours 30 minutes
12.00 noon to 12.45am
= 12 hours 45 minutes
Total time
= 17 hours 15 minutes
Total time in minutes
= (17  60) + 15 minutes
= 1035 minutes.
 Write 5.3 minutes in minutes and seconds.
5 minutes + (0.3  60) seconds = 5 minutes 18 seconds
 Write 345 minutes in hours and minutes.
345  60
= 5 hours and 45 minutes left over
= 5 hours 45 minutes
 How many seconds in 1.5 hours?
There are 3600 seconds in 1 hour
1.5  3600 = 5400 seconds
 What fraction of an hour is 25 minutes?
25
5
of an hour

60
12
 You also need to be able to calculate numbers of days in months and years and also
know what years a particular century spans.
 How many days are there between 15th January and 2nd April in a leap year?
There are 31 days in January, so 31 – 15 = 16
29 days in February in a leap year
31 days in March + 2 days in April
Total = 16 + 29 + 31 + 2 = 78 days.
3
Updated Feb 2013
 Remember that when centuries are named, e.g. fifteenth century, the name is given to
the century which will end in the year 1499. So the fifteenth century spans the years
1400 to 1499.
Time exercises
1.
How many minutes from 11.40 a.m. to 12.35 a.m?
2.
It is 10.36 p.m. What was the time 2 12 hours ago?
3.
How many minutes in 1 34 hours?
4.
How many seconds in 2 14 minutes?
5.
Write 2.2 minutes in minutes and seconds
6.
Write 280 seconds in minutes and seconds
7.
What fraction of an hour is 50 minutes?
8.
What percentage of 1 hour is 20 min?
9.
What time is 50 minutes after 4.45 p.m.?
10. A bus arrived 46 mins late at 2.34 p.m.? What time was it due?
11. If I left home at 7.43 a.m. and arrived at 2.35 p.m., how long did my journey take?
12. I start work at 7.45 a.m. and leave at 4.30 p.m. How long am I at work?
13. How many hours from 4 p.m.Tuesday to 11 a.m.Thursday?
14. How many hours in
2
3
of a day
15. What time is 11 hours before 4.30 p.m.?
16. Write 5.45 p.m. in 24 hour notation
17. Write 3.20 a.m. in 24 hour notation
18. It is 18.30 hours. What will be the time in 6 hours 30 minutes?
19. It is 11.00 hours. What was the time 13 12 hours ago?
20. If I study 2.5 hours every day, how many hours do I study in a week?
21. How many days from 12 July to 19 September?
4
Updated Feb 2013
22. How many weeks in
3
4
of a year?
23. How many days in June, July and August altogether?
24. If I sleep on average 8 hours every day,
a)
how many hours do I sleep in a year
b)
what percentage of my time do I sleep?
25. I get paid every fortnight. How many pays in a year?
26. How many days from February 20 to March 20 in a leap year?
27. How many years in 3.2 centuries?
28. What period does the seventeenth century span?
Time solutions
18) 01.00 hours
1) 12 hours 55 minutes
19) 21.30 hours
2) 8.06 pm
20) 17.5 hours
3) 105 minutes
21) 69 days
4) 135 seconds
22) 39 weeks
5) 2 minutes 12 seconds
23) 92 days
6) 4 minutes 40 seconds
1
5
7) 6
24) a) 2920 hours
25) 26
1
3
8) 33 %
26) 29 days
9) 5.35 pm
27) 320 years
10) 1.48 pm
28) 1600 to 1699
11) 6 hours 52 minutes
12) 8 hours 45 minutes
13) 43 hours
14) 16 hours
15) 5.30 am
16) 17.45 hours
17) 03.20 hours
5
Updated Feb 2013
b)
33 3
%
```