How to Calculate the Area of a Circle

Circles are simple closed curves. The common distance of any point on the circle from its center is called the radius. A line that passes through the center and whose points lie on the circle is called the diameter. Learn to calculate the area of any circle by following this simple equation.

Difficulty: Easy

Instructions

1. 

   To calculate the area of a circle, multiply Pi times the radius-squared, where Pi is 3.14 and radius is a given number represented by "R". In other words, Area = Pi * R-squared.

2. If you were asked to find the area of a circle whose radius was 9cm, you would simply plug this number into the formula.
   
   Area = Pi * R-squared
   Area = 3.14 * 9cm-squared
   Area = 254.34cm-squared

3. What if you were only given the diameter of the circle? Well, if you remember, the diameter is twice the radius in any given circle. Therefore, if you have a circle whose diameter is 12cm, you would know that the radius must be half of that number, so the radius would be 6cm.
   Now you can plug that number into the original formula and calculate the area of the circle.
   
   Radius = 1/2(Diameter)
   Radius = 1/2(12)
   Radius = 6
   
   Area = Pi * 6-squared
   Area = 3.14 * 36
   Area = 113.04cm-squared

Resources

• How to Calculate the Area of a Trapezoid

[goodselfme]

on 3/18/2009 You explain this like a good teacher would. TX 5*

[sonni57]

on 3/17/2009 Thanks for this article on how to calculate the area of a circle. Good reference.

[athome]

on 3/15/2009 You lost me at circles. lol 5*