Measure and calculate perimeter

Learning focus

Learn how to measure and calculate the perimeter of rectilinear shapes.

This includes:

  • a learning summary
  • one quiz
  • two videos
  • two interactive activities


Try this quiz to see how well you know the topic.


This video will help you to understand how to measure the perimeter of a shape. Why not make some notes as you watch the video to help you to remember later?

Calculating perimeter

The perimeter is the distance all the way around the outside of a 2D shape.

To work out the perimeter, add up the lengths of all the sides.

The perimeter of the shape shown is:

10 + 10 + 6 + 6 = 32

Perimeter of rectilinear shapes

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

They normally look like two or more rectangles that have been joined together.

Watch the video below from BBC Bitesize on finding the perimeter of a rectilinear shape when you don't know the length of every side.

The perimeter of a shape is the distance around the outside. How would you find the perimeter of this rectilinear shape?

Step 1: Find the lengths of the missing sides. Look at the values of the lines parallel to the missing lengths.

The missing sides have been labelled A and B on the diagram above.

  • A is parallel to the 10 cm and 4 cm side. If you put A and the 4 cm line together, it would be the same length as the 10 cm line. You could write this as 4 cm + A = 10 cm. We can solve this to find that A = 6 cm

  • B is parallel to the 5 cm and 3 cm line. If you put them both together, they would be the same length as B. So 5 cm + 3 cm = B. Therefore, B = 8 cm.

Step 2: Add up all the sides to find the perimeter.

4 cm + 5 cm + 8 cm + 10 cm + 3 cm + 6 cm = 36 cm


Activity 1

Work out the perimeter of the park

Add together all the sides to work out the perimeter of the park.

Activity 2

Work out the missing lengths

Use what you have learnt to work out the perimeter of the next park. Can you work out the lengths of the sides that are not marked?


Play Guardians: Defenders of Mathematica to learn more and sharpen your skills on this topic.

Guardians: Defenders of Mathematica

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