About the Circle Calculator
Find the diameter, circumference and area of a circle from its radius. This tool is free, works in your browser and needs no sign-up.
How to use the Circle Calculator
Enter the radius.
Formula used
Diameter = 2r. Circumference = 2πr. Area = πr².
Example
With Radius 5, the calculator shows: Area = 78.5398; Circumference = 31.4159; Diameter = 10.
Frequently asked questions
Is the Circle Calculator free to use?
Yes. It is completely free and you can use it as many times as you like.
How accurate is the Circle Calculator?
The calculator uses standard formulas, so the maths is exact. Real life results can differ because of fees, taxes, rounding or personal factors, so treat the answer as an estimate.
Do you store the numbers I enter?
No. All calculations run in your browser. The values you type are not sent to our server.
Disclaimer: results are estimates for information only. They are not financial, medical or professional advice.