Circle Area Calculator

Calculate the area using the radius, diameter, or circumference

Circle Area Calculator

A = π × r²

Radius (r): cm

A = π × (d / 2)²

Diameter (d): cm

A = C² / (4 × π)

Circumference (C): cm

The area of a circle is the space enclosed inside its edge. It comes up in architecture, engineering, and design whenever you work with round shapes: pipes, wheels, circular tanks, or any cylindrical cross-section.

The Formula

A = π × r²

A — area of the circle (cm², m², etc.)
π — the number pi, approximately 3.14159
r — radius: distance from center to edge

The radius is squared because area grows in two dimensions: doubling the radius quadruples the area. If you only know the diameter or circumference, use the alternative modes in the calculator above.

Step-by-Step Example

If the radius of the circle is r = 5 cm:
A = π × 5² = π × 25 ≈ 78.5398 cm²

Using the diameter d = 10 cm:
A = π × (10 / 2)² = π × 25 ≈ 78.5398 cm²