How to calculate octagonal dimensions

Written by marie mulrooney
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An octagon has eight equal sides and eight equal angles between those sides. The regularity of this geometric figure makes finding its dimensions relatively easy; if you know the length of one side, you automatically know the length of all its sides, and there are established mathematical formulas for computing an octagon's perimeter and area using just the knowledge of one side's measurement.

Skill level:
Easy

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Instructions

  1. 1

    Measure or calculate the length of one of the octagon’s sides.

  2. 2

    Multiply this number by eight.

  3. 3

    Note the result from Step 2 down as the octagon’s perimeter; don’t forget to include the units of measure. So if the octagon has one side that’s 5 inches long (and thus, by definition, all the other sides are 5 inches long as well), its perimeter is 5 * 8 = 40 inches.

  1. 1

    Measure or calculate the length of one of the octagon’s sides.

  2. 2

    Square this number—that is, multiply it by itself. So if we continue to use an octagon with side length of 5 inches as our example, we would have 5 * 5 = 25 inches.

  3. 3

    Multiply the result from Step 2 times 4.84 to get the octagon’s area. To continue our example, we have 25 * 4.84 = 121 inches as the area for our octagon. The complete formula is (side)^2 * 4.84, where (side) is the length of any one of the octagon’s sides.

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