Circle Calculator — area, circumference, radius

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สูตร

C = 2\pi r = \pi d

Circumference is the distance around the circle.

A = \pi r^2

Area is the space inside the circle.

Choose which measurement you know and enter it.
Press Calculate. Exact answers are given in terms of π, with decimals underneath.

Diameter = 2 × 5 = 10.

Circumference = 2π × 5 = 10π ≈ 31.415927. Area = π × 5² = 25π ≈ 78.539816.

π is irrational, so “25π” is the exact answer. The decimal below it is rounded.

Any unit works. Lengths come out in the same unit; area comes out in that unit squared.