The Lesson

The diameter of a circle is twice the radius.

How to Find the Diameter from the Radius

Finding the diameter from the radius is easy.


What is the radius of the circle, with radius 5 cm, below?



Multiply the radius, 5cm, by 2.
5 × 2 = 10 cm


The diameter of the circle is 10 cm.

Lesson Slides

The slider below shows another real example of how to find the diameter of a circle from the radius.

Interactive Widget

Here is an interactive widget to help you learn about finding the diameter of a circle from its radius.

What Is a Circle?

A circle is a shape containing a set of points that are all the same distance from the center. This distance is the radius. The diameter is the line through the center of the circle that has its endpoints on the circle.