Circle Calculator

Find the area, circumference, and diameter of a circle from its radius. Enter the radius.

Area
— sq units
Of the circle.

Usage Tip

Double the radius and the circumference doubles, but the area quadruples — area grows with the square.

THE MATH
area = π × radius²
circumference = 2 × π × radius
A circle is the set of points a fixed distance (the radius) from a center.
Area scales with the square of the radius; circumference scales linearly.
Enter the radius; diameter is twice the radius.
Results use pi to full precision.
Area is in square units, circumference in linear units.
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