How to Calculate the Area of a Circle Given the Radius
- 1). Find the length of the circle's radius. The radius is the distance from the point at the center of the circle to any of the points at its edge. It can also be found by dividing the circle's diameter by 2.
- 2). Square the value of the radius. A square is found by multiplying a value by itself. For example, if the radius of the circle is two inches, multiply by two to get a value of four.
- 3). Multiply the squared value by pi. If you have a calculator with a "pi" key, which would likely be marked by the pictured symbol, you can use it the same way you would another number key. Input the value of the squared radius, then press the multiplication key, the "pi" key and "=" or "enter." If your calculator has no "pi" key, you can multiply by 3.14 instead.
- 4). The number that results is the area of the circle in square units. The unit the answer is given in will use the same base unit as whatever the radius was measured in.