# Finding the Radius from the Diameter(KS3, Year 7)

homesitemapgeometryfinding the radius from the diameter
The radius of a circle is half of the diameter.

## How to Find the Radius from the Diameter

Finding the radius from the diameter is easy.

## Question

What is the radius of the circle, with diameter 10 cm, below?

## 1

Divide the diameter, 10 cm, by 2.
10 ÷ 2 = 5 cm

## Answer:

The radius of the circle is 5 cm.

## Lesson Slides

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

## Interactive Widget

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

## Why Is Knowing the Radius in Terms of the Diameter Useful?

Most of the properties of a circle - such as its circumference and area - can be expressed in terms of the radius or diameter. Most students remember the area of a circle with a radius r as: But what if you are told the diameter d instead? Divide it by 2 to find the radius. If you substitute d2 for r, a formula for the area of a circle in terms of the diameter can be found: how to find the area of a circle using the diameter

This page was written by Stephen Clarke.

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