How do you calculate circumference?
Worked examples: Circumference
The perimeter of a circular shape is the distance around the outside of it (the same as the
perimeter of other shapes). The circumference of circle can be calculated if you know the
correct formula.
The formula for the circumference of a circle is C= d.
What is the circumference of this circle?
C= d
Substitute the actual dimensions.
C =  x 600
C = 1884.9556mm
C = 1885mm
Most engineering problems use the diameter of the circle (because this is normally the
marked dimension on a drawing). If you are only given dimensions for the radius of the circle
you can still solve the circumference problem.
If the radius of this circle is 300mm
C =  x 2r
(Note that 2r = d, that is, 2 x radius = diameter)
C =  x 2 x 300 = 1884.9556mm
C = 1885mm
Activity sheet: How do you calculate circumference
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Circumference problems
1.
You have to cut some pipe which will cover the sharp edges on a circular piece of plate. The
plate has a diameter of 780mm. How much pipe will you need to cover the edge?
2.
What length of wire will you need to wrap once around a piece of round pipe with a diameter of
135mm.
3.
If you walk completely around the outside of a circular garden bed with a radius of 14 metres,
how far have you walked?
4.
A circular table top has a diameter of 2.25m. If trim is $1.70 a metre, how much will it cost to buy
trim to go around the edge of the table top?
5.
You have been asked to cut rubber tubing to cover a rod which will be bent into a circular
shape. How much rubber will you need to cut if the circular shape is going to have a diameter of
725mm?
Check your responses with the answers below.
Answers
(1) 2,4500mm
(2) 424mm
(3) 88 m
Activity sheet: How do you calculate circumference
(4) $12.02
(5) 2,278mm
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