Circle Calculator
Calculate circle area, circumference, and diameter. Enter any one value to find the others — all in your browser, instant results.
About the Circle Calculator
This circle calculator runs entirely in your browser. Choose what you know — radius, diameter, circumference, or area — and enter the value. The tool instantly derives the other three quantities using π.
Formulas used
- Diameter = 2 × radius
- Circumference = 2 × π × radius
- Area = π × radius²
Depending on the input type, the calculator first converts the value to a radius, then computes all four properties from it.
Frequently asked questions
Does this tool upload my data? No. All calculations happen locally in your browser.
Are decimals supported? Yes. Any positive real value works.
What happens with a negative or zero value? Negative or zero inputs are rejected — circle measurements must be positive.
How precise is π? The calculator uses JavaScript's Math.PI, which provides about 15 significant digits.