How to Calculate Area of an Octagon

Written by michael keenan
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How to Calculate Area of an Octagon
A stop sign is an example of an octagon. (illuminated stop sign image by leemarusa from

An octagon is an eight-sided figure, two-dimensional figure. You might need to find the area of an octagon is you were making a stop sign or if you were building an octagonal ring for an Ultimate Fighting Championship-style event. To calculate the area of an octagon, you need to know the length of the sides or the length of the radius of the octagon.

Skill level:
Moderately Easy

Things you need

  • Ruler
  • Calculator

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    Using the Side Length

  1. 1

    Measure the length of side of the octagon with the ruler.

  2. 2

    Square the length of the side. For example, if your sides are each 10 inches long, you would get 100.

  3. 3

    Multiply the result from Step 2 by 4.84 to calculate the area of the octagon. For example, you would multiply 100 by 4.84 to find that the area equals 484 square inches.

    Using the Radius

  1. 1

    Measure the radius with your ruler. The radius is the distance from the centre of the octagon to the point where any two sides intersect.

  2. 2

    Square the radius from Step 1. For example, if the radius equals 8 inches, you would get 64.

  3. 3

    Multiply the result from Step 2 by 2.828 to calculate the area. For example, you would multiply 64 by 2.828 to find that the area of the octagon equals about 180.992 square inches.

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