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`C = 2 * pi * "r" `

Enter a value for all fields

The **Circumference of a Circle** formula, C = 2πr, computes* Circle * the circumference (perimeter) of a circle as a function of the radius (r).

**INSTRUCTIONS**: Choose units, and enter the following:

- (r) Radius of the circle.

**Circumference (C):** The calculator returns the circumference (perimeter) of the circle in meters. However, this can be automatically converted to other length units via the pull-down menu.

The Math

The formula for the circumference or perimeter of a circle is:

where:

- r is the radius of the circle.
- π is the constant (3.141592653589....)

**Related Calculators:**

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