## The Lesson

The circumference of a circle is found using the formula:In the formula,

**r**is the radius of the circle. The image below shows what we mean by radius:

## How to Find the Circumference of a Circle Using the Radius

## Question

What is the circumference of a circle with a radius of 5 cm, as shown below?## Step-by-Step:

# 1

# 2

Substitute the radius into the formula. In our example, r = 5.

Circumference = 2 × π × 5 = 31.4 cm

## Answer:

The circumference of the circle with a radius of 5 cm is 31.4 cm## What Is a Circle?

A circle is a shape containing a set of points that are all the same distance from a given point, its center.## What Is Pi?

**π**is the symbol for pi.

**π**is how many times longer a circle's circumference is than its diameter. It is the circumference divided by the diameter:

**π**is the same for all circles, and is approximately equal to 3.14.