Perimeter of a parallelogram and a trapezoid

The perimeter is the sum of the lengths of all the sides. For quadrilaterals, that is always 4 sides.

Parallelogram

A parallelogram has its opposite sides equal: `a` and `b`. Therefore:

o = 2a + 2b = 2(a + b)

Example. A parallelogram with sides `a = 8 cm`, `b = 5 cm`:

o = `2 · (8 + 5) = 26 cm`.

Trapezoid

A trapezoid has four different sides: the bottom base `a`, the top base `c`, and two legs `b` and `d`. The formula is simply the sum:

o = a + b + c + d

Example. A trapezoid with `a = 10`, `b = 6`, `c = 7`, `d = 5` (cm):

o = `10 + 6 + 7 + 5 = 28 cm`.

Isosceles trapezoid

In an isosceles trapezoid both legs are equal (`b = d`), so:

o = a + c + 2b

Watch out for units

• All sides must be in the same units before you add them.
• If one is in cm and another in dm, convert first.

Try it yourself

• Perimeter of a parallelogram
• Perimeter of a trapezoid