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.