Circle Calculator

Circle Area Calculator

Calculate area, circumference, radius, and diameter from any one value. Get step-by-step solutions with unit conversions.

Known Quantity

Value

Unit

Calculator Features

Calculate circle area from radius or diameter

A = \pi r^2

Find the perimeter of the circle

C = 2\pi r = \pi d

Find radius from area or circumference

r = \sqrt{\frac{A}{\pi}}

A = \pi r^2 = \frac{\pi d^2}{4}

C = 2\pi r = \pi d

r = \sqrt{\frac{A}{\pi}}

r = \frac{C}{2\pi}

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Center to edge

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d = 2r

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Perimeter

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Space inside

Learn why πr² gives the area

Understand the circle perimeter formula

Calculate arc length and sector area