How to Calculate the Square Feet of a Circle

••• Bandolinata/iStock/GettyImages

Geometry can get confusing. Between calculating area, volume, circumference and all the other calculations, the formulas can get jumbled in your head. However, calculating the area of a circle is one of the basic formulas for geometry and not a hard one to master.

  1. Understanding Geometric Measurements

  2. 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.

  3. Area Formula

  4. 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, 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.

  5. Using Correct Measurements

  6. 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 .75 feet.

  7. Calculating Area

  8. 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: Area= πr2 or (3.14)(.75 ft)2. This becomes 3.14 x (.75 ft x .75 ft) = 3.14 x .5625 ft2= 1.77 ft2.


    • Though the math is easy enough to do by hand, a calculator will make it go quicker.


    • Make sure the units in your answer are squared. Otherwise, you aren't talking about area.


About the Author

James Rada, Jr. was a newspaper reporter for eight years and earned 23 awards from the Maryland Delaware D.C. Press Association, Associated Press, Society of Professional Journalists, Maryland State Teachers’ Association and CNHI. He also worked for 12 years as a marketing communications writer, earning a Print Copywriter of the Year Award from the Utah Ad Federation. He holds a Bachelor of Arts in communications.

Dont Go!

We Have More Great Sciencing Articles!