Circumference Calculator

Calculate the circumference of a circle using the radius, diameter, or area with the calculator below.


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How to Find the Circumference of a Circle

A circle is a round shape with no corners or straight edges where each point along its edge is the same distance from its center point. The circumference is the distance around the outside of a circle, also known as the perimeter of a circle.

If the path around the circle were flattened out into a straight line, the circumference would equal the line’s length.

diagram of a circle showing the radius, diameter, and circumference
Diagram showing the circumference of a circle

Circumference Formulas

You can find a circle’s circumference using a formula, depending on what you know about the circle.

Given the Radius

The radius is the length of a line from the center point of a circle to the outer edge. Given the radius of the circle, the formula for circumference is:

C = 2πr

The circumference C is equal to 2 times pi times the radius r of the circle r. Pi is a mathematical constant with an approximate value of 3.141592…

Graphic showing the circumference formula where C is equal to 2 times pi times the radius.

Given the Diameter

The diameter is the length of a line from an edge of a circle to the opposite edge. Given the diameter of the circle, the formula for circumference is:

C = πd

The circumference C is equal to pi times the diameter d of the circle d.

Given the Area

The area is the amount of space the circle occupies. Given the area of a circle, the formula for circumference is:

C = 2 × π × A ÷ π

The circumference C is equal to 2 times pi times the square root of the area A of the circle A divided by pi.

How to Find the Diameter From Circumference

It is possible to solve the diameter of a circle using the circumference. Since the diameter is equal to double the radius, use the inverse of the circumference formula to solve for the diameter.

d = C / π

Thus, the diameter d of a circle is equal to the circumference C divided by pi.

You might also be interested in our circle calculator for solving the other dimensions of a circle, including the radius, diameter, and area.