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
SEAGReady breaks perimeter of compound shapes into 2 steps, taught in order so each skill builds on the last.
supporting lesson — excluded from official-format mocks
Find the perimeter of an L-shape or compound shape when all outer edge lengths are labelled
supporting lesson — excluded from official-format mocks
Find the perimeter when some edge lengths must be calculated from given dimensions
Three free sample questions from our perimeter of compound shapes course. Every question comes with a full explanation, and hints that guide without giving the answer away.
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 Georgia's L-shaped card with all six boundary lengths labelled. How much ribbon does she need to go around it?
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.
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