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.

**Circumference of a Circle Formula**

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

∏ 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.

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∏.