Perimeter: what children learn
The perimeter of a shape is the distance all the way around its edge. Year 3 pupils learn to measure the perimeter of simple 2-D shapes by adding up the lengths of the sides.
In this game children find the perimeter of rectangles, squares and triangles. The lengths are given in centimetres, and every answer comes with the working, so children can see how the sides were added.
This topic covers the Year 3 statutory requirement in the National Curriculum in England (Measurement): pupils should be taught to “measure the perimeter of simple 2-D shapes”. Year 3 pupils are usually aged 7–8.
For families following US standards, the closest Common Core standard is 3.MD.D.8, which is taught in Grade 3.
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
- 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.
- 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.
- 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.
- Squares have 4 equal sides. A square with 4 cm sides has a perimeter of 4 + 4 + 4 + 4 = 16 cm.
Worked examples
Example 1: What is the perimeter of a rectangle 6 cm by 4 cm?
Working: 6 + 4 + 6 + 4 = 20.
Answer: 20 cm
Example 2: What is the perimeter of a square with 7 cm sides?
Working: 7 + 7 + 7 + 7 = 28.
Answer: 28 cm
Example 3: A triangle has sides of 5 cm, 5 cm and 6 cm. What is its perimeter?
Working: 5 + 5 + 6 = 16.
Answer: 16 cm
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
- Pupils 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 metres.
Free printable game and worksheet
The free printable starts with a game sheet, such as a colour-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
Is area taught in Year 3?
No. Year 3 is about perimeter. Area is introduced in Year 4 by counting squares.
Why are all the lengths whole centimetres?
Whole numbers keep the focus on what perimeter means. Decimal lengths come later.
Can it be played with a keyboard?
Yes. Press 1, 2, 3 or 4 to choose an answer.