Circle Area - Formula and Calculation Examples

There are three formulas for finding the area of a circle, depending on which measurement you already know: the radius, the diameter, or the circumference.

Using the Radius

When you know the radius, use this formula to find the area:

A = π × r²

Aarea of the circle πPI = 3.14159265… rradius of the circle r²radius squared

Using the Diameter

When you know the diameter, use this formula to find the area:

A = π × (d / 2)²

Aarea of the circle πPI = 3.14159265… ddiameter of the circle

Using the Circumference

When you know the circumference (perimeter), use this formula to find the area:

A = C² / (4 × π)

Aarea of the circle Clength of the circumference πPI = 3.14159265…

Visual representation of area

The image below shows how the area of a circle can be visualized using the radius:

Circle Area Formula

Using the Radius

Using the Diameter

Using the Circumference

Visual representation of area

More About the Circle