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
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
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