A circle is a two-dimensional object, which means that area is measured in units squared, such as square inches or square centimeters. To find the area of the circle, you only need to know the radius. The radius is the distance from the center of the circle to any point on the circle. Since all points on a circle are equidistant, it doesn't matter which point on the circle you use.
Measure the radius of the circle.
Multiply the radius by the radius. For example, if you have a 18 inch radius, you would multiply 18 inches by 18 inches to get 324 square inches.
Multiply the step 2 result by 3.1415, an approximation of pi, to find the circular area. Finishing the example, you would multiply 324 square inches by 3.1415 to get 1,017.846 square inches as the circular area.