What this covers
Perimeter is taught in Grade 3 (age 8 to 9) as a topic to introduce. It sits in the Measurement strand.
Worked example
Find the perimeter of a rectangle with length 8 cm and width 5 cm.
- Use the perimeter formula for a rectangle: P = 2 × (length + width).
- Add length and width: 8 + 5 = 13 cm.
- Multiply by 2: 2 × 13 = 26 cm.
Answer: 26 cm
Difficulty scale
The sheet generator offers five difficulty settings for this topic.
- Finding perimeters of simple polygons with all integer side lengths given.
- Finding perimeters of regular polygons given one side length, or rectangles given length and width.
- Compound rectilinear L-shapes requiring calculation of one or two missing side lengths.
- Shapes with decimal side lengths or algebraic expressions representing sides.
- Reverse problems (e.g. finding missing side given perimeter) and compound composite figures.
Common mistakes
- Confusing perimeter with area and multiplying length by width.
- Missing unlabelled internal or stepped edges when calculating the perimeter of compound shapes.
Curriculum links
Indicative matches to Common Core State Standards. Check wording and codes against the official document.
- 3.MD.D.8 Solve real-world problems involving perimeters of polygons, including finding unknown side lengths.