--- title: "Perimeter of Compound Shapes" description: "Measure and calculate the perimeter of composite rectilinear shapes in centimetres and metres" canonical: https://lightmysky.com/learn/mathematics/perimeter-of-compound-shapes-mt_n0AlyLQwC9 source: https://lightmysky.com/learn/mathematics/perimeter-of-compound-shapes-mt_n0AlyLQwC9.md retrieved: 2026-10-19 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Perimeter of Compound Shapes Measure and calculate the perimeter of composite rectilinear shapes in centimetres and metres Subject: Mathematics · Area: Measurement · Ages 9 to 10 Page: https://lightmysky.com/learn/mathematics/perimeter-of-compound-shapes-mt_n0AlyLQwC9 ## Ready when they can - Find the perimeter of an L-shaped figure by identifying all side lengths - Calculate the perimeter of a composite shape where some sides must be deduced - Draw a composite rectilinear shape with a perimeter of 40 cm ## Lesson: Perimeter of Compound Shapes You already know how to find the perimeter of a shape: add up the length of every side. A compound shape, like an L-shape, is made when two rectangles are joined together. To find its perimeter, add up every outside edge, even the short ones that make the step in the L. *(drawing: Compound shapes are built from simple shapes like this rectangle, joined edge to edge.)* Some sides in a compound shape have no number written on them. You can still work them out, because the short step sides must add up to match the long straight side facing them. **Example.** A shape is an L. Going around: bottom = 10 cm, right side (short) = 4 cm, top (short) = 4 cm, left side = 10 cm. Two step sides in the middle have no number. The bottom (10 cm) must match the two top pieces added together, so the missing top piece is 10 - 4 = 6 cm. The left side (10 cm) must match the two right pieces added together, so the missing right piece is also 10 - 4 = 6 cm. Now add all six sides: 10 + 4 + 6 + 6 + 4 + 10 = 40 cm. **Tip.** Count the sides before you add them up. It is easy to skip a short step side by accident, and every side counts toward the perimeter. **Recap.** To find the perimeter of a compound shape, add every outside side, working out any missing ones first. ## Practice 16 questions on this page, each with its working shown. ## Needs first - [Area of compound shapes](https://lightmysky.com/learn/mathematics/area-of-compound-shapes-mt_eMtV6tBSJm) - [Perimeters of polygons](https://lightmysky.com/learn/mathematics/perimeters-of-polygons-mt_WtcFrxGOgw) ## Opens up - [Perimeter (age 10+)](https://lightmysky.com/learn/mathematics/perimeter-age-10-mt_MJZA90uc6H)