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`c = 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.

**Circle Area**- Computes the area of a circle given the radius**(A = π r**.^{2})**Area of Circle Arc Segment f(r,θ)**- Computes the area of an arc segment of a circle given the radius (**r**) and angle (**θ**)**Area of Circle Arc Segment Area f(r,h)**- Computes the area of an arc segment of a circle given radius (**r**) and the depth (**h**) into the circle.**Area of Circle Sector f(r,Θ)**- Computes the area of a sector (pie slice) of a circle given the radius (**r**) and angle (**Θ**).**Angle of Circle Sector f(r,h)**- Computes the angle in a circle from the radius and depth of the chord.**Area of Circle Annulus**- Computes the area of an annulus (ring) given the inner radius (**r**) and outer radius (**R**).**Radius of Circle from Center and a Point**- Computes the radius of a circle given the center point (**h,k**) and any other point (**x,y**) on the circle.**Circumference of Circle**- Computes the circumference of a circle given the radius (**C = 2 π r**).**Circle Arc Length**- Computes the length of an arc length on a circle given the radius (r) and angle (**Θ**)**Circle within a Triangle**- 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**- Computes the radius of a circle that circumscribes a triangle given the length of the three sides (**a,b,c**) of the triangle.**Circle Diameter from Area**- Computes the radius and diameter of a circle from the area.**Circle Radius from Circumference**- Computes the radius of a circle given the circumference.**Circle Circumference from Area**- Computes the circumference of a circle given the area.**Circle Radius from Area**- Computes the radius of a circle given the area.**Chord Length**: Computes the length of a chord in a circle from the radius and height.**Circle Radius from Chord**- Computes the radius of a circle based on the length of a chord and the chord's center height.**Equation of Circle from Center and Point Coordinates**- Develops the general equation of a circle based on the coordinates of the center (h,k) and any point on the circle (x,y).**Circle with same Perimeter as an Ellipse**- Computes the radius of the circle with the same perimeter of an ellipse defined by the semi-major and semi-minor axes.**Rectangles to Cover a Circle**- Computes the number of rectangles needed to minimally cover a circle based on the circle's diameter and the length and width of the rectangles.