Circle Calculator
Enter the radius or diameter to calculate the circle's area, circumference, and diameter. Handy for math problems and design — all calculations happen inside your browser.
Enter the values to see the result.
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Area
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Circumference
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Diameter
How to use
- Choose the input basis (radius or diameter).
- Enter the value.
- The circle's area, circumference, and diameter are shown in real time.
Frequently asked questions
How do I find the area of a circle?
The area of a circle is pi (π) times the radius squared: area = π × radius × radius.
How do I find the circumference of a circle?
The circumference is the diameter times pi (π), equal to 2 × π × radius.
Are the values I enter sent to a server?
No. All calculations happen only inside your browser, and the values you enter are never sent to or stored on any server.