# How to Find the Area of a Circle Using the Diameter

## Finding the Area of a Circle Using the Diameter

The area of a circle is found using the formula:

In this formula, **d** is the diameter of the circle. The image below shows what we mean by diameter:

## Interactive Widget

Use this **interactive widget** to draw a circle and then calculate its area from the diameter. Start by clicking in the shaded area.

**Oops, it's broken!Turn your phone on its side to use this widget.**

## How to Find the Area of a Circle Using the Diameter

Finding the area of a circle using the diameter is easy.

### Question

What is the area of a circle with a diameter of 10 cm, as shown below?

### Step-by-Step:

# 1

# 2

Substitute the diameter into the formula. In our example, d = 10.

Area = π × 10^{2}⁄4

Area = π × 10 × 10 ÷ 4

Area = π × 100 ÷ 4

Area = π × 25

Area = 3.14 × 25

Area = 78.5 cm^{2}

### Answer:

The area of the circle with a diameter of 10 cm is 78.5 cm^{2}.

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

The area of a circle can be found using the radius rather than the diameter.

The area of a circle, using the radius, is found using the formula:

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

Read more about how to find the area of a circle using the radius