Circle Calculator
Calculate circle area, circumference, and diameter from a positive radius.
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How to use Circle Calculator
For radius r, area is πr², circumference is 2πr, and diameter is 2r. All lengths share the input unit.
- Enter radius.
- Check that the input follows the stated limits and uses consistent units.
- Run the calculator, review the result, then copy or download it.
Good to know
- Requires a positive radius. This models a flat Euclidean circle, not a spherical surface or ellipse.
- Decimal inputs have at most 120 characters and magnitude from 1e-100 to 1e15, or zero. Floating-point results are rounded to 12 significant digits; extreme derived results may underflow or be rejected. Exact integer results are identified separately.
Common questions
What calculation does Circle Calculator perform?
For radius r, area is πr², circumference is 2πr, and diameter is 2r. All lengths share the input unit.
Do I enter radius or diameter?
Enter radius, which is half the diameter. The result includes the diameter for comparison.
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