Perimeter

Perimeter: what children learn

In this game children find the perimeter of rectangles, squares and triangles. The lengths are given in centimeters, and every answer comes with the working, so children can see how the sides were added.

Supports part of Common Core 3.MD.D.8: finding the perimeter of polygons from their side lengths. This focused game does not cover the entire standard.

Common Core connection: 3.MD.D.8. This is focused practice for part of the standard.

How to play

Answer 10 questions before the clock runs out. Tap an answer, or press 1 to 4. Each game has 10 multiple-choice questions and a 150-second timer. A wrong answer shows the correct one before moving on. You earn up to three stars depending on your score.

Step by step

1. Walk round the edge. Perimeter means the whole way round. Imagine an ant walking along each side until it gets back to where it started.
2. Add every side. Add the lengths of all the sides. A triangle with sides 3 cm, 4 cm and 5 cm has a perimeter of 12 cm.
3. Rectangles have pairs. A rectangle has two long sides the same and two short sides the same. A 5 cm by 3 cm rectangle has a perimeter of 5 + 3 + 5 + 3 = 16 cm.
4. Squares have 4 equal sides. A square with 4 cm sides has a perimeter of 4 + 4 + 4 + 4 = 16 cm.

Worked examples

Common mistakes and how to fix them

• Adding only the two numbers shown on a rectangle. A rectangle has 4 sides. Write the missing two lengths on before adding.
• Multiplying the length and width. Multiplying gives the area, the space inside. Perimeter is the distance round the outside.
• Forgetting the unit. Perimeter is a length, so the answer is in cm or m.

Activities to try at home

• Measure round a book, a table or a photo frame with a tape measure.
• Walk round the edge of a garden or park and talk about its perimeter.
• Use string to go round a shape, then measure the string.

Ideas for the classroom

• Students measure the perimeter of shapes drawn on squared paper.
• Make different rectangles with a 20 cm perimeter using string or geostrips.
• Measure the perimeter of the classroom in meters.

Free printable game and worksheet

The free printable starts with a game sheet, such as a color-by-answer picture, an answer maze or a secret-code joke, followed by a worksheet. Both use the same checked questions as the online game, and the answers are on the last page. Print it, or save it as a PDF from your browser’s print menu.

Open the free printable game and worksheet

Frequently asked questions

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