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

## The Lesson

The diameter of a circle is found from the circumference of a circle using the formula:

In this formula, C is the circumference of the circle. The image below shows what we mean by finding the diameter from the circumference:

## How to Find the Diameter from the Circumference

Finding the diameter from the circumference is easy.

## Question

What is the diameter of the circle, with circumference 30 cm, below?

# 1

Diameter = Cπ
Don't forget: / means ÷ and π is pi (≈ 3.14)

# 2

Substitute the circumference into the formula. In our example, C = 30.
Diameter = 30π Diameter = 30 ÷ π Diameter = 30 ÷ 3.14 Diameter = 9.6 cm

The diameter of the circle is 9.6 cm.

## Lesson Slides

The slider below shows another real example of how to find the diameter of a circle from the circumference. Open the slider in a new tab

## Interactive Widget

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