Trapezoid Perimeter Calculator
A trapezoid has one pair of parallel sides (the bases) and two non-parallel sides (the legs). Its perimeter is simply the sum of all four side lengths, with no shortcut because the sides can all differ. Enter the two parallel sides, the two legs, and optionally the perpendicular height, and this calculator returns the perimeter and, when a height is given, the area as the average of the parallel sides times the height. These are exact geometric definitions; use consistent length units throughout.
Trapezoid formulas
Perimeter = a + b + c + d
Area = (a + b) / 2 x height
Midsegment = (a + b) / 2
Sum of parallel sides = a + b
The perimeter sums all four sides. The midsegment, which joins the midpoints of the legs, equals the average of the two parallel sides, and the area is that midsegment times the height.
Trapezoid geometry context
- A trapezoid has exactly one pair of parallel sides (the bases).
- The two legs may differ in length, so all four sides are summed for the perimeter.
- An isosceles trapezoid has equal legs and equal base angles.
- The midsegment equals the average of the two parallel sides.
- Area needs the perpendicular height, not a slanted leg length.
Trapezoid perimeter: frequently asked questions
How do you find the perimeter of a trapezoid?
Add the lengths of all four sides: the two parallel sides (the bases) and the two non-parallel sides (the legs). Perimeter P = a + b + c + d. A trapezoid has no equal-side shortcut in general, so every side must be measured and summed.
What is the area of a trapezoid?
The area is the average of the two parallel sides multiplied by the perpendicular height: A = (a + b) / 2 x h, where a and b are the parallel sides and h is the distance between them. This calculator computes the area when you also enter the height.
What is the difference between a trapezoid and a parallelogram?
A trapezoid has exactly one pair of parallel sides, while a parallelogram has two pairs. In a parallelogram opposite sides are equal, which gives a perimeter shortcut. A trapezoid's four sides can all differ, so its perimeter requires summing each side.
Does the height affect the perimeter?
No. The perimeter depends only on the four side lengths. The height is needed for the area, because area measures the space enclosed, not the boundary. If you do not enter a height, the perimeter is still correct and the area is shown as not available.
What is an isosceles trapezoid?
An isosceles trapezoid has its two non-parallel sides (legs) equal in length and base angles equal. Its perimeter is still the sum of all four sides, but with the two legs equal you only need three distinct measurements. The general formula here covers both isosceles and irregular trapezoids.
Official sources
- U.S. National Institute of Standards and Technology: Digital Library of Mathematical Functions.
- NASA: Geometry and area reference.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.