Calculate the Perimeter of a Range of 2D Shapes

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

In this activity, we'll be working out the perimeter of a range of different 2D shapes.

When working out the perimeter we must make sure that we check the unit of measure - is it measured in mm, cm, m, km, or something else?

Sometimes we need to use a ruler to work out the perimeter.

In this activity, we will be given some of the measurements, so we won't need a ruler.

We'll use the measurements we are given to work out those we don't know.

Let's get started.

Let's work out the perimeter of this rectangle.

The short side (height) is 15 cm long. 

The long side (width) is 30 cm long.

We have been given two of the measurements - 15 cm and 30 cm.

We know that the opposite sides will be equal.

So we can see that we have two sides of 15 cm = 30 cm.

We also have two sides of 30 cm = 60 cm.

Now we add these together to get the measurements of all four sides:

 30 cm + 60 cm = 90 cm

The perimeter of the rectangle is 90 cm. 

Now let's have a look at another 2D shape.

This is a regular hexagon.

If a shape is regular, it has sides that are all the same length.

If the sides of this hexagon are 7 cm each, what is the total perimeter?

Answer

We know that the sides are all the same length because the shape is regular.

We know that a hexagon has 6 sides.

So, we simply multiply 7 cm by 6.

7 cm x 6 = 42 cm

Now it's your turn to have a go.