Free online tool

Circle Calculator

Choose the known circle measurement and calculate every related dimension.

Radius-
Diameter-
Circumference-
Area-

Method

Geometry formulas

Each result is calculated from the dimensions entered using standard Euclidean geometry formulas. The tool checks required constraints such as the triangle inequality and positive lengths.

Unless a unit is explicitly selected, lengths use any consistent unit, areas use its square, and volumes use its cube.

Questions

Circle Calculator FAQ

What is the circumference formula?

Circumference is 2 times pi times radius, or pi times diameter.

What is the area of a circle?

Area is pi multiplied by the square of the radius.

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