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Watch: Finding the perimeter on a grid

The perimeter is the distance around a 2D shape. You can calculate the perimeter by adding up the lengths of all the sides.

Watch this video where Mr Smith explains how to find the perimeter on a grid. You can also practise finding the perimeter with a pencil and paper.

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Example 1

To work out the perimeter on a grid, let's look at this rectangle drawn on a square grid. Each square is worth 1 cm.

A grid with a rectangle with length 7 squares and sides 4 squares

To find the perimeter of the rectangle, you have to add up all of the sides.

By using the squares, you can work out how long each side is.

The length measures 4 squares or 4 cm.

The width of the rectangle measures 7 squares or 7 cm.

A rectangle drawn on grid labelled with length 7 cm and sides 4 cm

Add up all the sides.

7 cm + 7 cm + 4 cm + 4 cm = 22 cm

Another way to work out the perimeter on a grid is by counting the squares around the outside of the shape!

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Example 2

Molly has measured the perimeter of a football pitch. She says it has a perimeter of 26 m. Is she correct?

Bird's-eye view of a football pitch

Let鈥檚 check Molly鈥檚 answer by working out the perimeter on a grid.

Football pitch drawn as a rectangle on a grid.

Each square represents 1 m.

The length of the rectangle measures 8 squares or 8 m.
The width measures 5 m.

Now add up all 4 sides.

8 m + 8 m + 5 m + 5 m = 26 m

Molly was correct!

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Rectilinear shapes

How do you find the perimeter of a rectilinear shape?

A rectilinear shape is a shape that has straight sides that meet at right angles.

You can find their perimeter in exactly the same way as every other shape, you just have more sides to add up!

A rectilinear shape

Use the squares to help you work out its perimeter. Remember, each square is worth 1 cm.

A rectilinear shape with sides labelled: 6cm, 3cm, 5cm, 1cm, 1cm, 2cm.

Now you know the lengths of each side, it鈥檚 time to add them up!

6 cm + 3 cm + 5 cm + 1 cm + 1 cm + 2 cm

That鈥檚 a lot of numbers! To make it easier, you can add up a couple of the numbers first.

Calculation of 6cm + 3cm + 5cm + 1cm + 1cm + 1cm + 2cm and 9cm + 6cm + 3cm

6 cm + 3 cm + 5 cm + 1 cm + 1 cm + 2 cm or 9 cm + 6 cm + 3 cm = 18 cm

The perimeter of the rectilinear shape is 18 cm.

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Example 1

Can you find the perimeter of this shape?

Image gallerySkip image gallerySlide 1 of 4, Step 1. A rectilinear shape. Sides show 15cm, 6cm, 8cm and 3cm., First, you need to work out the lengths of the missing sides. Let鈥檚 focus on the horizontal lines first.
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Example 2

Work out the missing lengths of this shape to find the perimeter.

Image gallerySkip image gallerySlide 1 of 4, Step 1. A rectilinear shape. Sides show 7cm, 2cm, 6cm and 12cm., To begin, let's look at the missing horizontal length.
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Activities

Quiz 1

Test what you have learnt in this guide with this tap and find activity.

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Activity 2

Perimeter of the letters T and H

You will need a piece of paper and pencil for this activity.

On a piece of squared paper, draw your name in block letters. Try and draw your all your letters the same height.

Can you:

  • Predict which letter has the smallest perimeter?

  • Predict which letter has the largest perimeter?

  • Calculate the perimeter for each letter?

  • Calculate the total perimeter for your name?

Perimeter of the letters T and H
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Quiz 2

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More on 2D shapes

Find out more by working through a topic