Finding the perimeter of L-shapes and other compound rectilinear shapes by identifying and adding all outer edges.
Where your child meets this in real life: Measuring the boundary of an L-shaped room or calculating edging for an irregular garden
This topic isn't tested on its own, but it sits inside questions on tested topics. Each SEAG paper has 28 maths questions. Questions 29 to 50 are multiple choice with five possible answers, and questions 51 to 56 need a short written answer. With 56 questions in 60 minutes across English and maths, that is about a minute per question.
SEAGReady breaks perimeter of compound shapes into 2 steps, taught in order so each skill builds on the last.
Find the perimeter of an L-shape or compound shape when all outer edge lengths are labelled
Find the perimeter when some edge lengths must be calculated from given dimensions
Try three free questions from our perimeter of compound shapes course. They start easy and get harder, so you can see where your child's confidence runs out. If they manage the last one without a hint, this topic is probably secure. If not, the steps above show where to start.
The diagram shows Dylan's L-shaped bedroom. He wants to put LED lights around its complete edge. What total length of lights does he need?
The diagram shows an L-shaped swimming pool. What is its perimeter?
The diagram shows a stepped flower bed with all eight boundary lengths labelled. What is its perimeter?
This is the exact interactive worked example your child sees in SEAGReady. Step through it and watch the method build up.
Molly's bedroom is an L-shape. She wants to put fairy lights around the edge of her room. All six walls are labelled: 8m, 3m, 5m, 4m, 3m, 7m.
What is the total length of fairy lights she needs?
8 + 3 + 5 + 4 + 3 + 7
The perimeter is ONLY the outer boundary
Step 1 of 4
Molly's bedroom is an L-shape. She wants to put fairy lights around the edge of her room. All six walls are labelled: 8m, 3m, 5m, 4m, 3m, 7m.
What is the total length of fairy lights she needs?
Molly needs 30 metres of fairy lights.
The key insight: Perimeter means the OUTER boundary only - go all the way around the outside!
Common mix-up: Including internal lines in the count. Internal lines are not part of the perimeter - only count edges on the outside.
These are the misconceptions we see most often in perimeter of compound shapes, including the ones our practice questions are specifically designed to catch.
Struggling with perimeter of compound shapes? The real gap is often in one of these earlier topics.
Sitting the SEAG test this November? Read our last-month revision plan, Paper 1 vs Paper 2 and test day guide.
SEAGReady finds the exact step where your child gets stuck, teaches it with worked examples like the one above, and brings it back for review so it sticks.
Free to start · no card needed