11+ Maths: Compound Shape Perimeter Practice (CEM & GL)
21 October 2026
Understanding compound shape perimeter
Practising perimeter questions with compound shapes is an important part of 11+ maths revision. Compound shapes appear in both CEM and GL exams, so it helps to be confident with the method.
What is a compound shape
A compound shape is made by joining two or more simple shapes, such as rectangles or squares, to form a new figure. These shapes often have sides that touch or overlap, which can make perimeter questions tricky.
How to find the perimeter
Start by identifying all the outer edges of the shape. Only count the sides that form the outside boundary. Do not include any sides that are shared or hidden inside the shape. Add up the lengths of all the outer sides to find the perimeter.
Worked example
Imagine a compound shape made by joining two rectangles. The first rectangle is 5 cm by 3 cm. The second rectangle is 4 cm by 2 cm, joined along the 3 cm side of the first rectangle.
Step 1: Draw the shape and label all sides. Some sides will be joined and not part of the outer edge.
Step 2: List the outer sides. For this example: 5 cm (top), 4 cm (right), 2 cm (bottom right), 1 cm (bottom middle, as 3 cm - 2 cm = 1 cm), 5 cm (bottom left), and 3 cm (left).
Step 3: Add the outer sides: 5 + 4 + 2 + 1 + 5 + 3 = 20 cm.
The correct answer is 20 cm.
Tips for parents
Encourage your child to trace the outer edge with a finger or pencil to avoid missing or double-counting sides. Remind them to check for any sides that are hidden or shared between the joined shapes.
Key insight: Practising compound shape perimeter questions helps children avoid common mistakes and builds confidence for the 11+ CEM and GL exams.
