How to Find the Perimeter and Circumference

A non-circular shape's perimeter is determined by measuring the total length of its border.

A perimeter is the total length of the border of a closed figure. A circumference is the perimeter of a circular figure. The process of finding the perimeter of a non-circular figure, a figure with no round angles, is not the same process involved in finding the circumference of a circle; hence the difference between a perimeter and a circumference. In like manner, the formula for finding the circumference of a perfectly round figure is not the same formula used to find the circumference of a semi-circle.

Instructions

1. Measure each individual side of the figure using the same unit of measurement. Record each measurement. Add the measurements together. The result is the perimeter of the non-circular figure.

   Example - a rectangular figure with the following measurements:

   Base = 9 inches; Side One = 4 inches; Top = 9 inches; Side Two = 4 inches

   9 + 4 + 9 + 4 = 26

   Perimeter equals 26 inches

2. Measure the diameter of the circle. The diameter of a circle is a straight line passing through the center of a circle from one side of the figure to the other side. Multiply the diameter by pi. (Pi is equal to approximately 3.14.). The result is the circumference of a circle.

   Example: circle with a diameter of 21 centimeters

   21 * 3.14 = 65.94

   Circumference equals 65.94 centimeters

3. Measure the diameter of the semi-circle. Divide the diameter by 2. The result is the radius of the semi-circle. Multiply the semi-circle's radius by pi (3.14). The result is the circumference of a semi-circle.

   Example: semi-circle with a diameter of 14 inches

   14 / 2 = 7

   7 * 3.14 = 21.98

   Circumference equals 21.98 inches

References

• Arkansas Tech University: Perimeter and Area
• West Texas A&M University; "Beginning Algebra Tutorial Formulas"; Kim Seward
• City Colleges of Chicago: Perimeter and Circumference