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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.

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.

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.

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!

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

Let’s check Molly’s answer by working out the perimeter 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!

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!

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

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

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

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

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.

Can you find the perimeter of this shape?

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

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

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?