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`C = 2 * pi * "r" `

Enter a value for all fields

The **Circumference of a Circle** formula, C = 2?r, 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.
- ? is the constant (3.141592653589....)

**Related Calculators:**

**Circle Area**- This computes the area of a circle given the radius**(A = ? r**.^{2})**Segment Area f(r,?)**- This computes the area of an arc segment of a circle given the radius (**r**) and angle (**?**)**Segment Area f(r,h)**- This computes the area of an arc segment of a circle given radius (**r**) and the depth (**h**) into the circle.**Sector Area f(r,?)**- This computes the area of a sector (pie slice) of a circle given the radius (**r**) and angle (**?**).**Area of Annulus**- This computes the area of an annulus (ring) given the inner radius (**r**) and outer radius (**R**).**Radius -Center to a Point**- This computes the radius of a circle given the center point (**h,k**) and any other point (**x,y**) on the circle.**Circumference**- This computes the circumference of a circle given the radius (**C = 2 ? r**).**Arc Lengths**- This computes the length of a cord segment (arc length) on a circle given the radius (r) and angle (**?**)**Circle within a Triangle**- This computes the radius of a circle inscribed within a triangle given the length of the three sides (**a,b,c**) of the triangle.**Circle around a Triangle**- This computes the radius of a circle that circumscribes a triangle given the length of the three sides (**a,b,c**) of the triangle.**Radius from Circumference**- This computes the radius of a circle given the circumference.**Circumference from Area**- This computes the circumference of a circle given the area.**Radius from Area**- This computes the radius of a circle given the area.**Radius from Cord**- This computes the radius of a circle based on the length of a cord and the cord's center height.