A circle that measures 10 feet across has a radius of 5 feet. The diameter is the distance from one side of the circle to the other, passing through the circle's center. The diameter equals two times the radius, so the radius equals the diameter divided by two.

To discover the area of a circle, multiply pi times the radius squared. Finding the area of a 10-foot circle entails multiplying 3.14 x 25 for an area of 78.5 square feet. The circumference of a circle is the distance around the circle and is equal to pi times the circle's diameter. In a 10-foot circle, the circumference is 3.14 x 10, or 31.4 feet.