Everyday maths 2
Everyday maths 2

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Everyday maths 2

1.1 Perimeter of simple shapes

Described image
Figure 3 Finding the perimeter of simple shapes

In order to work out the perimeter of the shapes above, all you need to do is simply add up the total length of each of the sides.

  • Rectangle: 10 + 10 + 6 + 6 = 32 cm.
  • Triangle: 12 + 12 + 17 = 41 cm.
  • Trapezium: 10 + 12 + 10 + 18 = 50 cm.

When you give your answer, make sure you write the units in cm, m, km etc. One other important thing to note is that before you work out the perimeter of any shape, you must make sure all the measurements are given in the same units. If, for example, two lengths are given in cm and one is given in mm, you must convert them all to the same unit before you work out the total. It doesn’t usually matter which measurement you choose to convert but it’s wise to check the question first because sometimes you might be asked to give your answer in a specific unit.

Activity 1: Finding the perimeter

Work out the perimeters of each of the shapes below.

Remember to give units in your answer and to check that all measurements are in the same units before you begin to add.

  1. Described image
    Figure 4 Calculating the perimeter – Question 1
  2. Described image
    Figure 5 Calculating the perimeter – Question 2
  3. Described image
    Figure 6 Calculating the perimeter – Question 3


  1. 24 + 18 + 24 + 18 = 84 m.
  2. If you worked in cm:
    • 1.2 m = 120 cm.

      Therefore, the perimeter is 120 + 120 + 90 = 330 cm.

    If you worked in m:

    • 90 cm = 0.9 m.

      Therefore, the perimeter is 0.9 + 1.2 + 1.2 = 3.3 m.

  3. 50 mm = 5 cm, 62 mm = 6.2 cm.

    Therefore, the perimeter is 24 + 5 + 10 + 6 + 6.2 + 20 = 71.2 cm.

Hopefully, you found working out the perimeters of these shapes fairly straightforward.

The next step on from shapes like the ones you have just worked with, is finding the perimeter of shapes where not all the lengths are given to you. In shapes such as a rectangle or regular shapes like squares (where all sides are the same length) this is a simple process. However, in a shape where the sides are not the same as each other, you have a little more work to do.


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371