Circle Perimeter Formula

The perimeter of a circle is the length of its circumference — the curved outer edge. You can calculate it using either the radius or the diameter.

Using the Radius

When you know the radius, calculate the perimeter with this formula:

C = 2 × π × r

Cperimeter (circumference) πPI = 3.14159265… rradius of the circle

Using the Diameter

When you know the diameter, calculate the perimeter with this formula:

C = π × d

Cperimeter (circumference) πPI = 3.14159265… ddiameter of the circle

Both formulas give the same result, since d = 2 × r.

More About the Circle

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Circle Perimeter Formula

Using the Radius

Using the Diameter

More About the Circle

Circle Area
Formula