How to Calculate the Perimeter of a Decagon

Ten sides and 10 angles fit together to form a decagon. In a regular decagon, each angle measures 144 degrees, and all sides measure the same length. Irregular decagons have different sized angles and sides. Calculating the perimeter—or distance around—a decagon may seem challenging because of the number of sides. However, by following these simple steps, the perimeter of a decagon should prove easy to find.

Things You'll Need

• Ruler
• Paper
• Pencil

Instructions

What Type of Decagon?

1. Measure each side of the decagon. Record measurements next to each side.

2. Determine whether the decagon is regular or irregular. If the sides measure equally, the decagon is regular. If the sides measure differently, the decagon is irregular.

3. If the decagon is irregular, continue with this section. If the decagon is irregular, skip to Section 2.

4. Add together the lengths of all 10 sides of the decagon. The sum equals the perimeter of the decagon.

Regular Decagon

1. If the decagon is regular, record the following equation: "P equals 10 times S." "P" stands for the perimeter of the decagon, and "S" stands for the length of a side.

2. Substitute the measurement of one side for "S" in the equation. For example, if the length of a side is 5 inches, your new equation would read, "P equals 10 times 5 inches."

3. Solve for "P" by multiplying 10 by the length of the side. For example, if the length is 5 inches, then "P" will equal 50 inches.

References

• I Coach Math: Math Dictionary
• Math Open Reference: Perimeter of a Polygon