Perimeter

What does perimeter mean?

The perimeter is the distance all around a flat shape. Examples of flat shapes are squares, rectangles and triangles.

How do we find the perimeter of shapes?

Perimeter of a square

A square has four equal sides. To find the perimeter of a square, we can simply add the length of the four sides. Another way to find the perimeter of a square is to multiply the length of one side by four. Look at the example below.

Perimeter of a rectangle

A rectangle has four sides. The opposite sides are equal. We can find the perimeter of a rectangle by adding the length of all four sides.

We can also find the perimeter of a rectangle by adding the length to the width and then multiplying by two.

(length +width) x 2

Another way to find the perimeter of a rectangle is:

(length x 2) + (width x 2)

Look at the example below.

Watch this video which shows how to calculate the perimeter of a rectangle.

Perimeter of a triangle

Since a triangle has three sides, you can find the perimeter by adding the length of the three sides.

If the triangle has three equal sides, you can also find the perimeter by multiplying the length of one side by three.

Finding the perimeter of other shapes

For any shape you can find the perimeter by adding the length of all the sides. If all the sides of the shape are equal, you can also find the perimeter by multiplying the length of one side by the number of sides the shape has. For example, a hexagon has six sides. If each side of the hexagon is 5 meters long, the perimeter of the hexagon is 6 x 5m = 30m. Look at the example below.

Important tip: You must note the unit that is being used when you calculate perimeter. If meters are being used, then your answer must be in meters. If inches are being used, then your answer must be in inches. An answer with the wrong unit will be considered a wrong answer. An answer with no unit will be considered a wrong answer. In the example above if your answer was 30 cm or just 30 then it would be incorrect.

Watch this video which shows how to find the perimeter of different shapes.

Word problems about perimeter

Problem 1

Matt lives in a neighborhood with a rectangular courtyard. The courtyard is 20 meters long and 15 meters wide. What is the perimeter of the courtyard?

Note: The courtyard is a rectangle. Remember that the opposite sides of a rectangle are equal. Use any one of the methods for calculating perimeter of a rectangle. Also, remember that the unit we are using is meters (m).

Working:

Perimeter of the courtyard = (length + width) x 2

(20m + 15m) x 2 = 35m x 2 = 70 m

Problem 2

Jason draws a perfect square on a large piece of paper. One side of the square measures 40 centimeters. What is the perimeter of the square?

Note: Since we are dealing with a square, we need to use one of the methods for calculating the perimeter of a square. Also remember that the unit we are using is centimeters (cm).

Working:

Perimeter of the square = length x 4

40 cm x 4 = 160 cm

Note: We can also solve the two problems above by adding the length of all the sides. Try it!

Take the perimeter quiz!

Special thanks to Mr. Kerwin Eloise for contributing to this page.