Circles and circumference

Math

Definition

A circle is a set of all points in a plane that are the same distance (radius) from a center point. The circumference is the distance around the circle, calculated using the radius or diameter.

Examples

  • A bicycle wheel with a 14-inch diameter has a circumference of about 44 inches
  • Finding how much fencing is needed to enclose a circular garden
  • Calculating the distance traveled in one revolution of a merry-go-round
Key Fact

C = 2πr = πd; A = πr²

Related Terms

Arc length and sector area Central and inscribed angles Area of polygons

Study This Concept

Practice circles and circumference with free review games in these units:

Pre-Algebra Unit 9: Area and Perimeter