Calculate the Perimeter of Simple 2D Shapes

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

 

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

 

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 most of the measurements, so we won't need a ruler.

We'll need to work out some measurements using the information we have been given.

 

Let's get started.

 

Let's work out the perimeter of this rectangle.

 

                

 

We know that the shape is a rectangle.

We have been given two of the measurements - 15 cm and 10 cm.

We know that the opposite sides will be equal.

 

So we can see that we have two sides of 10 cm = 20 cm.

We also have two sides of 15 cm = 30 cm.

 

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

 20 cm + 30 cm = 50 cm

 

The perimeter of the rectangle is 50 cm.

 

Now it's your turn to have a go.