How to Calculate Circle Area: πr² Formula with Examples

The area of a circle is the total space inside the circle. It is calculated using the constant π (pi), which is approximately 3.14159.

Circle Area Formula

Area = π × r²

Where r is the radius (distance from the center to the edge) and π ≈ 3.14159.

Example

A circle with a radius of 5 cm:

• Area = 3.14159 × 5² = 3.14159 × 25 = 78.54 cm²

Using the Diameter

If you know the diameter (d), divide it by 2 to get the radius: r = d ÷ 2.

Example: diameter 10 cm → r = 5 → Area ≈ 78.54 cm².

Using the Circumference

If you know the circumference (C), find r = C ÷ (2π) first, then compute the area.

Real-World Uses

• Round tables or rugs
• Circular pools or ponds
• Design and engineering work

Try the circle area calculator for instant results.