How to Measure the Perimeter of a Circle

Physical Measurement

• 1

  Use a ribbon or thread to place over the circle's edge or line.

• 2

  Mark the point on the ribbon or thread where it meets its starting end.

• 3

  Stretch the ribbon or thread straight along a ruler.

• 4

  Read the value on the ruler where you marked the ribbon or thread. This is the perimeter, or circumference, of the circle.

Measuring by Calculation

• 5

  Use a ruler to measure the diameter of the circle, which is the distance across the circle that passes through the center.

• 6

  Measure the farthest distance between either side of the circle if the center of the circle is not marked.

• 7

  Multiply the diameter of the circle by the value of pi, which is approximately 3.14. For example, if the circle's diameter is 5 inches, the calculation would be 5 inches x 3.14 = 15.7 inches.