CircumferenceLesson #33

What is Circumference?

The distance around the outside of a circle is called the circumference (essentially, it is the perimeter of a circle)

diameter

Circumference

How do we calculate

circumference?In order to calculate the circumference, you must know the radius or diameter of the circle (radius is half the diameter)

diameter

Pi is used to calculate

circumferenceIn order to calculate the circumference, you must multiply the diameter of the circle by Pi (3.14)

If you only have the radius multiply that by two to get the diameter

Formulas for circumference:

C = π d

Circumference = Pi (3.14) x diameter

or

C = 2πr

Circumference = 2 x Pi (3.14) x radius

ExampleIf the diameter of the circle is 18 cm….

diameter

C = π dCircumference = Pi (3.14) x diameter

C = 3.14 x 18C = 56.5 cm

ExampleIf the radius of the circle is 12 cm….

diameter

C = 2πrCircumference = 2 x Pi (3.14) x radius

C = 2 x 3.14 x 12C = 75.36 cm

orC = π dCircumference = Pi (3.14) x diameterDiameter = 2 x 12 = 24

C = 3.14 x 24C = 75.36 cm