How to Find the Radius Using the Area

A circle's radius extends from its origin, or center, and reaches to its circumference. The area of the circle is the part of the circle encapsulated by the circle's circumference. These two identifying characteristics of a circle are interrelated and each can be discovered using the other as a tool. Using the circle's area to calculate its radius can illustrate the relationship of the two properties and help in understanding the circle as a whole.

Instructions

1. Divide the circle's area by pi, which is the mathematical constant 3.14. For example, if the circle's area is 28.26 inches squared, then dividing it by 3.14 results in 9.

2. Find the square root of the product of the area divided by pi. For the example, the square root of 9 is 3. The radius of the circle is 3.

3. Multiply the radius by 2 to obtain the diameter. For the example above, the 3 doubled is 6. The diameter of the circle is 6.

References

• Math Goodies: Area of a Circle

Resources

• Scientific Illustrator: Circle Calculator