Perimeter of compound shapes
for 5th grade

How to calculate the perimeter of compound shapes

A compound shape is a shape made up of 2 or more basic shapes that are joined together. You can think of the shape of a capital L as being a compound shape made up of 2 rectangles at right angles to each other. The procedure for calculating the perimeter of a compound shape is as follows:

1. Identify the individual shapes that make up the compound shape.
2. Measure the length of each side of the individual shapes and add them together to find the perimeter of each shape.
3. Add the perimeters of all the individual shapes together.
4. Subtract the lengths of any sides that are shared by more than 1 shape.

For example, if a compound shape is made up of a square with sides of length 2 cm and an equilateral triangle with sides of 2 cm, it's perimeter will be:

2 cm x 4 (the square)
plus
2 cm x 3 (the triangle)
minus
2 cm (their shared side)
= 12 cm

Notes on this topic

This topic asks you calculate perimeters in terms of x where x represents some length with a given unit.

Use a slow game like 4 in a row to practice this topic first, then when you get into a timed game like Pong, you will have had enough practice to be able to work out the questions really fast!