Circumference is the distance around a circle, which equals a little more than three times its diameter:
The actual ratio of the circumference of a circle to its diameter is known as pi written as π. The approximate value of π is 3.14. To find the circumference C of a circle, multiply the diameter d of the circle by 3.14 (an approximation of π). The formula for finding the circumference of a circle may be written as:
C = π × d or C = πd
See also perimeter, pi.