How do I find circle area from diameter?

A = π × (d/2)² = πd²/4. Divide diameter by 2 to get radius, then use A = πr².

What is the area of a circle with radius 10?

A = π × 10² = 100π ≈ 314.16 square units.

How do I find radius from area?

r = √(A/π). Divide the area by π, then take the square root.

How to Calculate the Area of a Circle

The area of a circle measures the space enclosed within it. This is one of the most fundamental geometric formulas used in math, engineering, and everyday life.

Area of Circle Formula

A = π × r²

Where:

A = Area of the circle
π = Pi (approximately 3.14159)
r = Radius of the circle

Step-by-Step:

1
Find the radius
If given diameter, divide by 2 to get radius.
2
Square the radius
Multiply the radius by itself (r × r).
3
Multiply by π
Multiply r² by π (3.14159) to get the area.

Worked Examples:

Garden circle

r: 5 meters

Result: 78.54 sq meters

A = π × 5² = π × 25 = 78.54 sq meters

Pizza

diameter: 12 inches

Result: 113.1 sq inches

r = 12/2 = 6. A = π × 6² = 113.1 sq inches