For a review of basic circle terms, please see Circle Area tips.

The circumference (C) of a circle is the distance around the circle.

r = radius d = diameter C = circumference   diameter = 2 × radius d = 2 r Circumference = 2 π × radius = π × diameter C = 2 π r C = π d

Example 1: Area answer in terms of π

Find the circumference in terms of π. Type "pi" in for π so that a correct answer would look like 7pi m Circumference:

Since we know the radius, use the circumference equation C = 2 π r.

C	=	2 π r
	=	2 π (28 mi)
	=	56 π  mi

The answer is   Circumference:

Example 2: Area answer with π = 22/7

Find the area. Use 22/7 as an approximation for π. A correct answer would look like 14.5 cm.

Using the same problem as Example 1, we know that the circumference C

C	=	56 π  mi
	=	56 ( )  mi
	=	856 ( )  mi
	=	176  mi

The answer is   Circumference: