The area of a circle is determined by the formula: A = π r2. You can easily calculate the area of a circle in under a minute. All you need is a calculator, a circle to measure and a tool with which to measure, such as a ruler.
Determine the radius of the circle
Use a ruler or similar tool to measure the radius of the circle. This is the length of the line from the middle of the circle to any point on its edge.
Convert the radius to feet
If the radius of the circle was measured in inches, multiply the number by 0.0833333 using the calculator. If it was measured in centimeters, multiply the number by 0.0328084.
Use the formula to calculate the area
Multiply the radius (in feet) by itself. Then multiply this number by pi (approximately 3.141592). There should be a pi (π) button on your calculator to make this easier. This number is the area of the circle in square feet.