How to Calculate the Perimeter of a Circle

The perimeter of a circle is most commonly referred to as the circumference of a circle and we will use the word circumference for our explanation below.

Diameter of a Circle

Look at this diagram, here you can see the diameter – the distance from one side of the circle to the other side.

circle-diameter

Circumference of a Circle Formula

Now to calculate the circumference of the circle we multiply pi (∏) by the diameter (d) of the circle.

circle-circumference-formula

∏ is a fixed value equal to 3.14, or to be exact 3.1415926535897932384 but = 3.14 will do for our calculations.

Calculating the circumference using diameter.

We now know what the diameter is and the formula to use so now let’s calculate the circumference.

circle-circumference-calculation3

And there you have your answer, the circumference of a 10cm diameter circle is 31.4cm. If you want to be really exact you could leave your answer as 10∏.