Trapezoid Perimeter Calculator — P = a + b + c + d
Enter all four sides of a trapezoid — the two parallel bases (a and b) and the two legs (c and d) — to find the perimeter instantly. For an isosceles trapezoid the calculator also derives the height from the legs.
P = a + b + c + d — sum of all four sides
- 1
Sum of the two bases
10 + 6 = 16 - 2
Sum of the two legs
5 + 5 = 10 - 3
Perimeter P = a + b + c + d
16 + 10 = 26
How does this calculator work?
The perimeter of a trapezoid = a + b + c + d, where a and b are the two parallel bases and c and d are the non-parallel legs. No height needed. The midsegment = (a + b) / 2. For isosceles trapezoids (c = d), height = √(c² − ((a−b)/2)²).
Formula
How this is calculated
A trapezoid (trapezium in British English) is a quadrilateral with exactly one pair of parallel sides, called the bases. The two non-parallel sides are called legs. The perimeter is simply the total length of the boundary: P = a + b + c + d, where a and b are the parallel bases and c and d are the legs. No height measurement is needed — unlike the area formula, the perimeter only depends on the four side lengths.
The midsegment (also called the median or midsegment) connects the midpoints of the two legs. Its length is always exactly half the sum of the bases: Midsegment = (a + b) / 2. This value equals the average width of the trapezoid.
When the trapezoid is isosceles (c = d), the calculator can also derive the perpendicular height from the legs using h = √(c² − ((a − b)/2)²). This is the right triangle formed by the leg, the height, and the horizontal projection of each base overhang. The height is shown as a bonus stat only when the inputs are consistent with an isosceles trapezoid.
Frequently asked questions
You need all four side lengths: the two parallel sides (bases a and b) and the two non-parallel sides (legs c and d). Unlike the area, the perimeter does not require the height.
Not without additional information such as the total perimeter, an angle, or the height. With three sides and the height, you can use the Pythagorean theorem to find the fourth side if the trapezoid is isosceles.
The midsegment connects the midpoints of the two legs. Its length equals (a + b) / 2 — the average of the two bases. The area can also be written as Midsegment × height.
Also known as
TG we-Calculate Editorial Team. (2026). Trapezoid Perimeter Calculator — P = a + b + c + d [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/trapezoid-perimeter-calculator
TG we-Calculate Editorial Team. "Trapezoid Perimeter Calculator — P = a + b + c + d." TG we-Calculate. 2026. https://we-calculate.com/calculator/trapezoid-perimeter-calculator.
TG we-Calculate Editorial Team, "Trapezoid Perimeter Calculator — P = a + b + c + d," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/trapezoid-perimeter-calculator
@misc{wecalculate_trapezoid_perimeter_calculator, title = {Trapezoid Perimeter Calculator — P = a + b + c + d}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/trapezoid-perimeter-calculator}}, year = {2026}, note = {TG we-Calculate} }
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