How to Find the Radius of a Circle From Its Circumference

Calculate the radius of a circle using its circumference.

A circle can be defined as a geometric shape in which all edges are the same distance from the center. The distance around the circle is known as the circumference, while the circle's radius is the distance from the center of the shape to any of its edges. By using 3.14, a number referred to in mathematics as "Pi," you can correctly calculate the radius of any given circle as long as you know its circumference.

Instructions

1. Know the formula for calculating circumference, radius and diameter: C = 3.14 x d. In this formula, "C" represents the circle's circumference, and "d" represents its diameter, which is the distance across the circle. The radius of a circle is always half of the circle's diameter.

2. Divide the circumference of the circle by 3.14 to get the diameter. For example, if the circumference of your circle is 20 centimeters, you would divide 20 by 3.14. The resulting number, 6.37, represents the circle's diameter.

3. Divide the diameter by 2 to find the radius. In the above example, the diameter of the circle is 6.37. When you divide 6.37 by 2, you get 3.19. Thus, 3.19 centimeters is the radius of a circle with a circumference of 20 centimeters.

Tips & Warnings

• You may use the formula C = 3.14 x d to calculate the radius or diameter of a circle using its circumference, and you may also use the formula to calculate a circle's circumference using its radius or diameter.

References

• Math Goodies/Gisele Glosser: Circumference of a Circle

Resources

• Math.com: Scientific Calculator
• University of California, Irvine/David Eppstein: Geometry in Action