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Math

Circle Area Calculator

Calculate circle area, circumference and diameter from its radius.

Exact method explained belowEditable inputs

Set up your calculation

Runs on your device

SOLUTION

Your result

Let’s calculate.

Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter radius.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

The method, explained

Area = πr². Circumference = 2πr. Diameter = 2r. Keep the same length unit throughout the calculation.

A WORKED EXAMPLE

A radius of 5 gives an area of about 78.54 square units, circumference of 31.42 units and diameter of 10 units.

What to keep in mind

Enter radius, not diameter. If your radius is in centimeters, the area is in square centimeters. Results use the available numerical approximation of π.

Common questions

What if I know the diameter?

Divide the diameter by two, then enter that value as the radius.

Does changing length units also change area units?

Yes. An area conversion squares the length conversion factor. Use Area Converter to convert the resulting square units.

Methodology maintained by ClarityKit. How these tools are built and checked.