**Radius**

An alternative method for calculating the circumference is by using the radius of the circle. The radius of a circle is the distance from the center to the edge of the circle. The radius equals half the diameter.

**Calculating the circumference using the radius.**

If we have the radius of a circle then to calculate the circumference we multiply pi (∏) by the radius (r) of a circle and then multiply by 2.

For the circle above we have a radius (r) of 5cm, so lets calculate the circumference:

And again we have the same answer, the circumference of a 5cm radius circle is 31.4cm. Again, if you want to be really exact you could leave your answer as 10∏.