How To Find the Area of a Circle

A circle is a simple two dimensional shape consisting of a set of points in a plane that is equidistant from a given point called the center. The surface within a circle is called the area of the circle. The distance around the edge of a circle is called the circumference.

A straight-line passing through the center of the circle touching the circumference of the circle at any two points is called the diameter. This is the largest distance between any two points on the circle. A straight-line drawn from the center of the circle to any point on its circumference is called the radius. The radius is half the diameter.

A circle is one of the most interesting and highly symmetric shapes. It is the shape with the largest area for a given length of perimeter. A circle's circumference and radius are proportional. The area enclosed and the square of its radius are proportional.

The area of a circle pi times the square of the radius. pi is the ratio of the circumference of a circle to its diameter, so that the circumference of a circle is pi times the diameter, or 2 pi times the radius. The symbol pi is approximately equal to 3.141592654 or 22/7. For finding the area of a circle, first find the square of the radius. Then multiply it by pi. If the instructions say "leave in terms of pi", then just stick the pi onto your number. If the instructions say anything about rounding, replace pi with 3.14 or make use of your calculator's pi button.

If the diameter is given, divide it by the number 2 for getting the radius. Alternatively you can use the diameter directly. For this, first find the square of the diameter and then dive it by 4. Next multiply it by pi.

For very large numbers, it is difficult to find the precise measurements. When calculating and measuring, take this into consideration. It is handy to have a calculator with you.