Perimeter of Compound Shapes: Step-by-Step Example
23 October 2026
When your child is learning about perimeter, compound shapes can seem tricky at first. By breaking the process into simple steps, you can help them see exactly what to do.
This example uses two rectangles joined together, so your child can follow along and understand how to find the perimeter of a compound shape. The method shown here is ideal for children preparing for the 11+.
Worked example
A compound shape is made from two rectangles joined together. The first rectangle is 4 cm long and 2 cm wide. The second rectangle is 3 cm long and 2 cm wide. They share one 2 cm side.
Step 1: Draw the shape. Label all sides.
Step 2: List all the outside sides you need to add. That is 4 cm + 2 cm + 3 cm + 2 cm + 3 cm + 2 cm.
Step 3: Add the sides: 4 + 2 = 6. 6 + 3 = 9. 9 + 2 = 11. 11 + 3 = 14. 14 + 2 = 16.
Key insight: Do not count the shared side in the middle. Only add the outside edges.
The correct answer is 16 cm.
After working through this example, your child will recognise which sides to add and how to avoid counting shared lines in the middle. They are now ready to practise more perimeter of compound shapes questions, using the same clear steps.
