About the Circle Calculator
Enter a circle’s radius, diameter, circumference or area and get all the others instantly.
Also known as: circle area, circumference calculator, radius calculator, diameter calculator, area of a circle, circle area calculator.
How to use this calculator
- Enter i know the, value.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
A = πr² · C = 2πr · d = 2r
Worked example
Using the values pre-filled in the calculator above:
- I know the: Radius
- Value = 5
the calculator returns:
- Area: 78.539816
- Radius: 5
- Diameter: 10
- Circumference: 31.415927