Irregular Trapezoid Area Calculator
Compute the area and perimeter of an irregular (scalene) trapezoid: enter the two parallel sides, the perpendicular height, and the horizontal offset of the top base to control leg asymmetry.
Area = (a + b) / 2 × h — depends only on the parallel sides and height
- 1
Average of the two parallel bases
(10 + 6) ÷ 2 = 8 - 2
Multiply by height
8 × 4 = 32Area = (a + b) / 2 × h — independent of leg shape.
How does this calculator work?
An irregular trapezoid's area is (a + b)/2 × h — just the average of the two parallel sides times the perpendicular height, regardless of leg shape. The legs are found via the Pythagorean theorem from the height and the horizontal projection of each leg.
Formula
How this is calculated
A trapezoid has exactly one pair of parallel sides, called the bases (a and b). The area depends only on the two bases and the perpendicular height h — it is always (a + b) / 2 × h, regardless of the shape of the legs. An irregular trapezoid has legs of unequal length and base angles that are not necessarily equal.
The legs are computed from the Pythagorean theorem. If the longer base a lies along the x-axis and the top base b is shifted horizontally by an offset x from the left, the left leg has length √(x² + h²) and the right leg has length √((a − b − x)² + h²). The perimeter is the sum of all four sides. Base angles are the acute angles each leg makes with the longer base.
Note that the area formula holds for any value of the offset x (including negative offsets where the leg overhangs the opposite side), as long as the two bases remain parallel and the height is the perpendicular distance between them.
Frequently asked questions
An irregular (or scalene) trapezoid has two parallel sides like any trapezoid, but the two legs (non-parallel sides) have different lengths and the base angles are not equal. An isosceles trapezoid is the special case where both legs are equal.
The offset controls how the top base is positioned relative to the bottom base. When x = 0, the left leg is vertical. Positive x shifts the top to the right, lengthening the left leg and shortening the right. This controls the leg asymmetry without changing the area.
No — the area (a + b)/2 × h depends only on the two bases and the perpendicular height. Sliding the top base horizontally (changing the offset) reshapes the legs and angles but leaves the area unchanged.
Also known as
TG we-Calculate Editorial Team. (2026). Irregular Trapezoid Area Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/irregular-trapezoid-area-calculator
TG we-Calculate Editorial Team. "Irregular Trapezoid Area Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/irregular-trapezoid-area-calculator.
TG we-Calculate Editorial Team, "Irregular Trapezoid Area Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/irregular-trapezoid-area-calculator
@misc{wecalculate_irregular_trapezoid_area_calculator, title = {Irregular Trapezoid Area Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/irregular-trapezoid-area-calculator}}, year = {2026}, note = {TG we-Calculate} }
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