Circle Calculator
Calculate area, circumference and diameter from the radius.
Result
Results are estimates for general information only and are not professional advice.
Circle measurements
From a circle's radius you can find its area (π × r²), circumference (2 × π × r) and diameter (2 × r). Enter the radius and this calculator returns all three at once.
Frequently Asked Questions
What is the Circle Calculator?
Calculate area, circumference and diameter from the radius. It runs instantly in your browser and is completely free to use.
What do I need to enter to use the Circle Calculator?
The Circle Calculator asks for a single value: Radius. Enter it and the result appears immediately — the calculation runs on your own device, so nothing you type is sent to a server.
How accurate is the Circle Calculator?
The Circle Calculator uses standard, widely-accepted formulas, so its figures are reliable estimates for everyday planning. They are not a substitute for advice from a qualified professional.
Is the Circle Calculator free, and do I need an account?
Yes. The Circle Calculator — and every other calculator on Calculatis — is completely free, with no registration, no download and no limit on how often you use it.