Circumference Calculator

Find the circumference of a circle from its radius.

Last updated: 25 Aug 2026

Quick answer

The circumference of a circle is 2 × π × radius. For example, a radius of 7 gives a circumference of about 43.98 units. Enter the radius above to calculate.

Radius

Find the circumference (perimeter) of a circle using C = 2 × π × r.

How to calculate circumference

1 Enter the radius.
2 We apply C = 2 × π × r.
3 The circumference appears instantly.

Frequently asked questions

What is the circumference formula?

Circumference = 2 × π × radius (or π × diameter).

How do I get it from diameter?

Multiply the diameter by π.

Is circumference the same as perimeter?

Yes — for a circle, the perimeter is called the circumference.

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Area of a Circle Calculator Area of a Rectangle Calculator Pythagoras Theorem Calculator