Calculate Perimeter by Finding Missing Measures

In this activity, we'll find the perimeter of shapes by using the measurements provided to work out those that we're not given.

Perimeter is the distance around the outside of a shape.

Sounds a little tricky, but it's nice and easy.  Let's have a look.

This shape has eight sides.

The lengths of six sides are provided.

We know that opposite sides of a rectangle are equal.

Even though it is not a rectangle, we can see that the lines along the top of the shape equal 7 m (5 + 2)

The lines across the bottom will also equal 7 m so the missing bottom length is 4 m (7 m - 3 m) 

The lines down the left side equal 4 m (1 m + 3 m)

The lines down the right will also equal 4 m, so the missing length is 2 m (4 m - 2 m)

Now we have all the measures, we simply need to add them together.

5 + 2 + 2 + 2 + 4 + 3 + 3 + 1 = 22 m

​We must remember to put the unit of measure, in this case, metres (m)

Top Tip:

It can help to mark each side as we add them. 

This means we won't miss any out or count them twice!

Now, why don't you have a go at some questions?