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`"Circle"_(perimeter) = 2 * pi * sqrt( "A" /pi)`

Enter a value for all fields

The **Circumference from the Area of a Circle** calculator computes the circumference of a circle based on the circle's area (A).

**INSTRUCTIONS:** Choose your preferred area units and enter the following:

**A**- the Area of the circle

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

The formula for the circumference of a circle from the area is as follows:

`c = 2π·sqrt(A/π)`

where:

- c is the circumference of the circle
- A is the area of the circle.

A circle is the set of all points equal in distance from a center point. This formula uses a form of the equation for the area of a circle to compute the circumference.

- Area: A = π • r
^{2}. - Therefore we know that `r = sqrt(A/pi)`.
- We also know that circumference of a circle is a function of the radius (C = 2 • π • r),
- therefore: `c = 2 * pi * sqrt(A/pi)`

If you know the area you wish to enclose, in a circular fence for example, this formula will tell you the circumference of the circle which is the length of the fence.

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