Circle Radius From Area Calculator

Enter a circle area to instantly find its radius, diameter, and circumference, shown with a clear diagram.

Input

Enter a circle area to work back to its radius, diameter, and circumference.

Area S

Radius r

3.989423

Diameter d

7.978846

Circumference C

25.066283

The length unit matches the square root of the area unit you entered.

The area S and radius r of a circle are related by S equals pi times r squared, where pi is about 3.14159.
Solving for the radius gives r equals the square root of S divided by pi, so you can find the radius from the area.
The diameter is twice the radius (d equals 2r) and the circumference is C equals 2 pi r.
Enter a positive number for the area. Values of zero or below, or non numeric input, return an error.
The length unit matches the square root of the area unit. If the area is in square centimeters, the radius is in centimeters.

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