Most commonly associated with the shape of a "Stop" sign, the octagon has eight sides that are equal in length. The circumference of an octagon, also known as the perimeter, can be calculated by using a simple mathematical formula and a length measuring device such as a tape measure.
Measure one side of the octagon using a tape measure. Because each side of the octagon should measure the same length, taking the measurement of one side should suffice for finding the circumference.
Multiply the length you measured by 8 or simply add up all eight sides. The answer should be the same and give you the circumference of the octagon shape. For example, if one of the sides of the octagon measures 3 inches, the circumference of the octagon would be 24 inches -- 3 x 8 = 24 or 3 + 3 + 3 + 3 + 3 + 3 +3 + 3 = 24.
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Convert the unit value of the circumference to another length measurement unit, such as feet and meters. You can use an online length conversion tool or complete the conversion mathematically. For example, if the circumference of your octagon was 24 inches, it would equal 2 feet because there are 12 inches in each foot.