Perimeter of Compound Shapes

Perimeter is the distance all the way around the outside of a flat shape. To find it, trace around the edge and add up every side length you pass. This works for any shape, even a tricky L-shape or a shape with a corner cut out. Just make sure you count every single side once and don't skip any hidden ones. For shapes made of rectangles pushed together, some side lengths might not be labeled. You can often figure out a missing side by comparing it to the sides you already know, like subtracting a small notch from a longer side.

You can find the perimeter of a shape drawn on a grid by counting the unit squares along the outside edge. For a rectangle, count the squares along each side and add the four totals together. For an irregular or L-shaped figure, trace all the way around the outline, counting one unit for every square edge you cross, until you get back where you started. This is a handy way to double check your answer when you calculate perimeter by adding side lengths, especially for composite shapes made of several rectangles joined together.

The perimeter of a shape is the total length of its outline, like a fence running all the way around a yard. To find the perimeter of any shape, including a composite shape made from rectangles, add up the length of every single side. There is no single formula for oddly shaped figures like L-shapes, so the safest method is always the same: find each side length, then add them all together. If a side length is not given, look for clues, like two shorter sides on the same line that must add up to a longer side you already know.

Area Builder is a fun online activity where you build flat shapes out of little squares, and the computer measures the area and perimeter for you right away. Try the challenge mode: it gives you a target perimeter, like 40 cm, and you drag squares around until your shape matches it exactly.