Perimeter

The perimeter of a shape is the distance around the outside.

It is a length so is measured in mm, cm, m, km or any other unit of length.

Question

Calculate the perimeter of this triangle:

A triangle with sides equal to 9 mm, 7 mm, and 6.5 mm

Add up the lengths of all the sides:

9 mm + 6.5 mm + 7 mm = 22.5 mm

Question

Calculate the perimeter of this rectangle:

A rectangle with sides equal to 14 cm and 5 cm
  1. Fill in the lengths of the missing sides: 14 cm and 5 cm
  2. Add the lengths of all the sides: 14 cm + 5 cm + 14 cm + 5 cm = 38 cm
Question

Calculate the perimeter of this L shape:

An L-shape with sides equal to 10 m, 3 m, 6 m, and 6 m

1. Calculate the lengths of the missing sides.

An L-shape with sides equal to 10 m, 3 m, 6 m, 6 m, and 4 m

The total height of the shape is 10 m, subtracting 6 m leaves us with the length of the missing edge of 4 m.

An L-shape with sides equal to 10 m, 3 m, 6 m, 6 m, and 9 m

The total width is missing – this has been split up into 3 m and 6 m. By adding them together we find the missing edge is 9 m.

2. Add all the lengths together:

3 m + 6 m + 6 m + 4 m + 9 m + 10 m = 38 m

Question

Fencing is sold in 2 m panels for £30 each. How much would it cost to fence this field?

A shape with sides equal to 14 m, 7 m, 20 m, and 5 m
  • Calculate the perimeter: 5 m + 14 m + 7 m + 20 m = 46 m
  • Calculate how many units of fencing is needed: 46 m ÷ 2 m = 23
  • Calculate how much 23 panels will cost: 23 × £30 = £690