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AA.2 Find the perimeter of polygons

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What is the perimeter of a polygon?

Perimeter is the total distance around a two-dimensional shape. For a polygon, the perimeter is the sum of the lengths of all its sides.

Example:
  • A triangle with side lengths 3 cm, 4 cm, and 5 cm → Perimeter = 3 + 4 + 5 = 12 cm
Note

Think of walking all the way around the outside of a shape. The distance you walk is the perimeter.

How do you find the perimeter of a polygon?

To find the perimeter of a polygon, add the lengths of all the sides. For regular polygons (where all sides are equal), multiply the length of one side by the number of sides.

Steps:
  • List all the side lengths.
  • Add them together to get the total.
  • If the polygon is regular, use: Perimeter = side length × number of sides.
Note

Always check if all sides are given. If not, you may need to use the properties of the shape to find missing lengths.

Examples of finding perimeter

Here are some worked-out examples to help you see how perimeter is calculated for different polygons.

Examples:
  • Rectangle with sides 6 m and 4 m → Perimeter = 6 + 4 + 6 + 4 = 20 m
  • Square with side 5 in → Perimeter = 5 × 4 = 20 in
  • Regular hexagon with side 8 cm → Perimeter = 8 × 6 = 48 cm
  • Pentagon with sides 3 ft, 4 ft, 5 ft, 4 ft, 3 ft → Perimeter = 3 + 4 + 5 + 4 + 3 = 19 ft
Note

Always label your final answer with the correct unit (cm, m, in, ft, etc.). Perimeter is a measurement of length, not area.

Things to remember

When working with perimeter, be careful to use correct operations and check your units.

Helpful Tips:
  • Double-check that you added all sides.
  • For regular polygons, multiplication saves time.
  • Keep units the same before adding (for example, convert inches to feet if needed).
Note

Perimeter problems are often word problems. Look for phrases like “distance around,” “border,” or “fence” to know you should find the perimeter.

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