1. Circumference Lesson #33

2. What is Circumference? The distance around the outside of a circle is called the circumference (essentially, it is the perimeter of a circle) diameter

3. 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

4. Pi is used to calculate circumference In 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

5. Formulas for circumference: C = π d Circumference = Pi (3.14) x diameter or C = 2πr Circumference = 2 x Pi (3.14) x radius

6. Example If the diameter of the circle is 18 cm…. diameter C = π d Circumference = Pi (3.14) x diameter C = 3.14 x 18 C = 56.5 cm

7. Example If the radius of the circle is 12 cm…. diameter C = 2πr Circumference = 2 x Pi (3.14) x radius C = 2 x 3.14 x 12 C = 75.36 cm or C = π d Circumference = Pi (3.14) x diameter Diameter = 2 x 12 = 24 C = 3.14 x 24 C = 75.36 cm