A circle has a radius of 5 cm. Find the circumference of the circle. (Take π = 3.14.)
Circumference = 3.14 × 10 = 31.4 cm
Ans: 31.4 cm
Example 1
A round mat has a radius of 21 cm. Find the circumference of the mat. (Take π = 22/7.)
Circumference = 22 × 6 = 132 cm
Ans: 132 cm
How to solve it
The circumference is the edge, all the way round. Rolled out flat, it is 3 diameters and a bit more, and pi counts that.
Write the rule: a circumference is pi times the diameter.
Find the diameter. The radius is 5 centimetres, so double it: 2 times 5 is 10 centimetres.
Put in the value of pi the question tells you to take: 3.14 times 10 is 31.4 centimetres.
With pi as 22 over 7 and a radius of 21, double first to get 42, then 22 over 7 times 42 is 132 centimetres.
A circumference is the edge, rolled out flat. Rolled out, it is 3 diameters and a bit more. That is what pi counts. So a circumference is pi times the diameter, and a radius is only half a diameter.
Practice questions with worked solutions
Question 1 is free to try. The other 7 open in the free trial, each with its full working.
How do you solve circumference of a circle questions in P6?
Circumference is the distance once round a circle.
What your child learns here
Circumference is the distance once round a circle. This page shows why it is pi times the diameter and how to use the rule with either value of pi. It sits under Area and Circumference of Circle in the Primary 6 syllabus, and it is the length every later perimeter question with curves depends on.
Understand pi as the number of diameters that fit once round the rim, a little more than 3.
Find a circumference as pi times the diameter, doubling a given radius first.
Keep a circumference as a length in cm or m, separate from an area in square units.
Treat one full turn of a wheel as one circumference when finding a distance travelled or a number of turns.
Work back from a circumference to the diameter by dividing by pi, and halve only when the radius is asked for.
Does the answer make sense?
When the answer is once round the circle, it must be a little more than 3 times the diameter; a diameter your child works back from a lap must be a little less than a third of that lap. A circumference is a length in cm or m, never square units.
How to practise these questions
The Basic questions train the circumference as π times the diameter, which means doubling a radius first. Intermediate questions add counting how many turns a wheel makes on a journey, and working back from a circumference to a diameter. Challenge questions keep only whole turns, or wrap something round a circle several times. If rolling out the circle does not click, read the written step-by-step solution.
Questions parents ask
What is the difference between circumference and perimeter? Circumference is the perimeter of a whole circle, the distance once round its edge. For a semicircle or a quarter circle, the perimeter is part of the circumference plus the straight edges, which other pages in this chapter cover.
Does my child need to remember that pi is about 3.14? Questions give the value to use, 3.14 or 22/7, or ask for an answer in terms of pi. What helps most is knowing that pi means a little more than 3 diameters, because that gives a quick size check on every answer.
When do children learn circumference in Singapore? In Primary 6. The MOE syllabus places area and circumference of circle in the Primary 6 Area and Volume sub-strand.
