Understand the type of measurement you are calculating. The three types of geometry measurement you may make are linear, area and volume measurements. They are easy to distinguish from each other. Volume measurements will have a final answer that is cubed, such as cubic feet or ft³. An area measurement will have a final answer that is squared, such as square inches or in². Linear measurements will have no exponents with their units in the final answer. Since we are seeking square feet, you know that we are calculating the area of a circle.

Write the formula down. Use the formula πr² to find the area of a circle. To understand what the formula means, you need to understand the variables. Pi, written as π, approximately equals (22÷7), usually rounded to 3.14. Pi is a universal constant that shows up naturally in calculations with round objects. The second variable, ​r​, stands for radius. Radius is the measurement from the center of the circle to the edge. To find the area of the circle, the radius will be squared before being multiplied by π.

Take your measurement. Since you want to have an answer in square feet, you need to use feet as your basic unit for measurement. This means when you measure the radius of your circle, you need to convert the radius to feet. For instance if your radius measures 9 inches, you convert from inches to feet by dividing the radius by 12 because there are 12 inches in a foot. So your radius measurement of 9 inches equals 0.75 feet.

Calculate the area. Using the above example, we can calculate the area of a circle with a 9-inch radius. First, plug in the information:

This becomes