Perimeter of Polygons
Skill: Finding perimeter by adding side lengths, including an unknown side
Download PDF worksheetAnswer key (PDF)
Free for personal and classroom use. Print at 100% / "Actual size" on US Letter paper.
About this worksheet
Perimeter is the distance all the way around a shape. This third-grade worksheet gives students practice finding the perimeter of six polygons: two rectangles, a square, a triangle, a pentagon, and a hexagon. Every side is labeled with its length and unit, and students add the side lengths to find the total. Two word problems at the end ask students to work backward and find a missing side length when the perimeter is already known.
The shapes use a mix of units, including centimeters, inches, feet, and meters, so students remember to include the correct unit in each answer. The shapes are not drawn to scale, which encourages students to rely on the labels rather than on how big a side looks.
How to use it: show students how to put a small check mark next to each side as they add it, so no side is counted twice or skipped. For rectangles, point out that opposite sides are equal, which can make adding faster (8 + 8 + 3 + 3). For the word problems, a sketch helps.
The answer key gives every perimeter and missing side with units. This worksheet supports Common Core standard 3.MD.D.8 (solve real world and mathematical problems involving perimeters of polygons, including finding the perimeter given the side lengths and finding an unknown side length).
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