Diameter and radius

The diameter of a circle is the distance from one side of a circle to the other through the centre.

The radius is the distance from the edge of the circle to the centre.

Circle with diameter and radius labelled

The diameter is twice as long as the radius.

Example

The pizza has a radius of 16 cm. What is the diameter?

Cookie with radius, 16cm

16 \times 2 = 32~\text{cm}