How to Find the Perimeter of a Trapezoid

Instructor: Maria Airth

Maria has a Doctorate of Education and over 20 years of experience teaching psychology and math related courses at the university level.

Trapezoids are a special type of geometrical figure. In this lesson, learn the steps to find the perimeter of a trapezoid through examples. You will also learn the different definition of trapezoid in the U.K.

Perimeter of a Trapezoid

When learning how to find the perimeter of a trapezoid, we really need to start with the definitions of these two terms:

  • Trapezoid: a four sided shape with two parallel sides
  • Perimeter: the measure of the outer edge of a shape

Let's try a problem. What is the perimeter of this trapezoid?


Step 1:

Remember that perimeter is the measure of the outer edge of a shape, or otherwise, the sum of the measures of the sides of the trapezoid. Representing the perimeter by P, and the sides as a, b, c and d, our formula is P= a + b + c + d.

Step 2:

Substitute the known values of the sides into the formula.

  • P= 2 + 5 + 3 + 7

Step 3:

Calculate the result.

  • P= 17

Step 4:

Make sure to format your answer to match the given information in the original problem.

  • 17 in.


The perimeter of the given trapezoid is 17 in.

U.K. Version and Another Example

U.K. Version

The definition of a trapezoid is slightly different in the U.K. (and members of the Common Wealth) than it is in the U.S. Trapezium is the word used for a four sided shape with exactly two parallel sides (the same as the U.S. trapezoid). However, a trapezoid in the U.K. is a four sided shape with no parallel sides (in the U.S., this is called a trapezium). It is a bit confusing, but if you remember that in the U.K. they drive on the 'other side' of the road, it may help you to remember that their definition of trapezoid is the 'other definition'.

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