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About the Circle Calculator
This calculator computes the key properties of a circle from a single known value. Enter a radius, diameter, circumference, or area and it returns all the others at once. Each result comes with the formula used, so you can see how the number was produced.
The tool applies the standard circle formulas: area = π × r², circumference = 2 × π × r, and diameter = 2 × r. You only need one measurement to start. Keep every value in the same unit, since the output inherits the unit you enter. If you measure in centimeters, the area comes back in square centimeters.
- Select the property you already know, such as radius or circumference.
- Type the value and pick a matching unit.
- Press calculate and read the area, circumference, diameter, and radius with their formulas.