Area Calculator: Compute Dimensions of a Circle

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Below is a circle area calculator, which will compute the linear dimensions radius, diameter, and circumference if you know the circle's area.

Do you know a different dimension? Instead try one of the other circle dimension calculators:

Radius Calculator

What is a Circle's Area?

The area of a circle is the space that is enclosed within its boundaries, as defined above.

If you drew a perfect circle using a marker, then switched colors and filled in the circle completely - the color you switched to would be the circle's area.

Dimensions of a Circle

Area, as defined above, is all the space contained inside the circle. It's straightforward to compute the area (or the opposite) from any of the linear dimensions below, but here's how to find the radius from a circle's area:

r = \sqrt{(a/\pi)}
Dimensions of a circle: O - origin, R - radius, D - diameter, C - circumference (Wikimedia)

Three lengths are most commonly applied:

  • The radius – the distance from the circle's center or origin to the edge
  • The diameter – the distance from edge to edge of a circle passing through its origin or center. Twice the length of a circle's radius
  • The circumference – the length of the outside boundaries of the circle

To find the area from the radius, it's very easy

a=\pi r^2

Diameter is just 2x radius, so to get the circle's area from the diameter:

a=\pi (d/2)^2

And to find area from circumference, it's easiest to first conve

r=c/2\pi \\ a = \pi r^2

Using the Circle Area Calculator

You can enter the area and then compute the lengths diameter and circumference in mils, inches, feet, yards, miles, millimeters, centimeters, meters and kilometers.

We'll allow area inputs in a ton of units. Choose: square mils, square inches, square feet, square yards, square miles, acres, hectares, square millimeters, square centimeters, square meters, and square kilometers.

To run the computations, hit the 'Calculate Circle Dimensions' button when you have entered the known radius.

Like this? Visit our other calculators and tools.

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