Mathematics, Statistics & Geometry

Circumference Calculator

Find the circumference of a circle from radius, diameter, or area with instant formulas, steps, diameter, radius, and area outputs.

Circumference
31.416
Radius5
Diameter10
Area78.54
Calculation StepsKnown radius: 5 Circumference = 2 * pi * 5 = 31.415927

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How to find circumference

The circumference is the distance around the outside edge of a circle. If you know the radius, use C = 2 * pi * r. If you know the diameter, use C = pi * d.

For a partial circle, use the arc length calculator. For 3D round objects, use the volume of a sphere calculator.

C = 2 * pi * r = pi * d

Where:
C=
Circumference of the circle
r=
Radius
d=
Diameter

Circumference from radius

C = 2 * pi * r

If the radius is 5:

C = 2 * pi * 5 = 31.4159

Circumference from diameter

C = pi * d

Because diameter is twice the radius, this is the same formula written in a shorter form.

Circumference from area

If you only know area, solve for radius first:

r = sqrt(A / pi)

Then use C = 2 * pi * r.

Frequently Asked Questions

The circumference formula is C = 2pir when using radius, or C = pi*d when using diameter.

Multiply the diameter by pi. For example, a diameter of 10 has circumference 31.4159.

First calculate radius with r = sqrt(area/pi), then calculate circumference with C = 2pir.

Circumference is the perimeter of a circle: the total distance around its outer edge.

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