How to find the perimeter of a shape, if the shape is drawn on centimetre squared paper.

Perimeter Video

Perimeter is the distance around the outside of a 2D shape. If the shape is drawn on centimetre squared paper all you need to do is go round the edge of the shape counting each edge of the shape. It’s a good idea to keep track of how many squares you have counted by marking each edge with a line or a small dot. Let’s take a look at a couple of examples:

Example 1

Work out the perimeter of this shape. Assume that the shape is drawn on centimetre squared paper.

The perimeter of the shape is 14 cm as there are 14 edges around the shape (all the edges have been marked with a small red dot).

Example 2

Work out the perimeter of this shape. Assume that the shape is drawn on centimetre squared paper.

The perimeter of the shape is 16 cm as there are 16 edges around the shape (like example 1, all the edges have been marked with a small red dot).

However, if the shape is not draw out on centimetre squared paper, then the perimeter of the shape can be found by adding up all the side lengths up. Make sure all the side lengths have been found before you start working out the perimeter.

Example 3

Work out the perimeter a rectangle that is 29 feet in length and 13 feet wide.

Here, you just need to add up all the side lengths to calculate the perimeter.

Perimeter = 29 + 29 + 13 + 13

Perimeter = 58 + 26

Perimeter = 84 feet

Another way to work this out is to add up the length and width, then double your answer.

Perimeter = (29 + 13) × 2

= 42 × 2

= 84 feet

As you can see, both ways give the same answer for the perimeter of the rectangle.

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Comments 1 comment

Joanna 4 years ago

Why don't you add any questions about the perimeter?

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