ScientificCalcul

Circle Circumference Calculator

Enter a circle radius to calculate circumference as an exact multiple of π and a decimal length, with the formula C = 2πr shown step by step.

Circle circumference calculator using 2 times pi times radius

Use this circle circumference calculator when a problem asks for the distance around a circle from its radius.

The result keeps pi in exact form and also gives a decimal approximation in the same length unit as the radius.

Learn the concept

Try these examples

  • r = 24.5
  • r = 9.6
  • r = 3.125

Quick reference

  • Circle circumference from radius: C = 2πr.
  • Circle circumference from diameter: C = πd.
  • The diameter is twice the radius: d = 2r.

FAQ

What is the formula for circumference from radius?

Use C = 2πr, where r is the circle radius.

What if I know the diameter instead?

Use C = πd. Because d = 2r, this is the same formula written with the diameter.

Sources and review

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