This area of a circle calculator will figure out the area of any circle given the radius, the diameter, or the circumference of the circle.

### Terminology

- "Area" - The amount of surface covered by a two dimensional shape. It is expressed in square units of measurement, for example square feet, square meters, square inches, square yards, etc.

- "Circumference" - The total distance around the outside edge of a circle.

- "Diameter" - The distance of a straight line that extends from edge to edge of the circle while passing through the center of the circle.

- "Radius" - The distance of a straight line that extends from the center of the circle to the edge of the circle.

### Calculating the Area of a Circle Using Radius

If you know the radius of a circle, you can calculate the area based on the following formula:

A = ϖ r^{2}

where

A = Area

ϖ = Pi = 3.14159265...

r = Radius

### Calculating the Area of a Circle Using Diameter

If you know the diameter of a circle, you can calculate the area based on the following formula:

A = ϖ ( d / 2 )^{2}

where

A = Area

ϖ = Pi = 3.14159265...

d = Diameter

### Calculating the Area of a Circle Using Circumference

If you know the circumference of a circle, you can calculate the area based on the following formula:

A = C^{2} / 4ϖ

where

A = Area

ϖ = Pi = 3.14159265...

C = Circumference