Circumference of a Circle Video

Diameter, Radius, and Circumference of a Circle

The distance around a circle is called the circumference. The distance across a circle through the center is called the diameterpi.gif is the ratio of the circumference of a circle to the diameter. Thus, for any circle, if you divide the circumference by the diameter, you get a value close to pi.gif. This relationship is expressed in the following formula:


where c.gif is circumference and d.gif is diameter. You can test this formula at home with a round dinner plate. If you measure the circumference and the diameter of the plate and then divide c.gif by d.gif, your quotient should come close to pi.gif. Another way to write this formula is: circum_formula.gif where · means multiply. This second formula for finding the circumference of a circle is commonly used in problems where the diameter is given and the circumference is not known (see the examples below).

For more help, check out our Circumference of a Circle Lesson Plan

Credit goes to: Mometrix Academy