How to Compute the Area of a Circle

To compute the area of a circle, use this formula: Area equals pi times the radius of the circle squared (A=pi*r*r). If you do not have a graphing calculator with a pi button, use 3.14 for an estimate.

Things You'll Need

• Calculator with a pi button
• Ruler or appropriate measuring tool (optional)

Instructions

1. Find the radius of the circle. If you are not given the radius, use the diameter to find it. The diameter is any straight line that passes through the center of a circle. If you are measuring a circular table, for example, use a tape measure to find the diameter and divide this length by 2. This is the radius.

2. Multiply the radius by itself, also known as squaring the radius. If the radius is 3 inches, calculate 3 times 3 to get 9.

3. Multiply the square of the radius by pi. For example, if the radius is 3 inches, multiply 9 times pi to get 28.2743338823. . . . That is the area of the circle. If you do not have a button on your calculator for pi, use the estimate 3.14. In this case, the area of the circle is 28.26 square inches.

4. Round to as many decimal places as needed. For example, if a homework problem requires rounding to 2 decimal places, then the area is 28.27 square inches.

5. Leave the answer in pi form if an exact answer is required. For example, when the radius is 3 inches, the exact area is 9pi square inches.

References

• Calculate Me: Calculate the Area of a Circle
• Blurtit.com: How Do I Define the Diameter of a Circle?