Grade 3 · Math · Lesson 23

Measure Perimeter of Polygons

The perimeter of a shape is the total distance around its outside edge. To find the perimeter, add up all the side lengths. For regular shapes (where all sides are equal), you can multiply one side length by the number of sides. Sides can be measured in inches (in) or in centimeters (cm) — the math is the same in both unit systems. The answer is in the same unit as the sides.

What this lesson teaches

1Calculate perimeter by adding all side lengths in inches and in centimeters
2Solve perimeter problems for squares, rectangles, and other polygons in US customary and metric units

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