Trapezoid Area Calculator
Enter the two parallel sides and the height of a trapezoid to find its area.
units
units
units
- 1
Sum of parallel sides
8 + 5 = 13 - 2
Midline (average base)
13 ÷ 2 = 6.5 - 3
Area = midline × height
6.5 × 4 = 26
Formula
How this is calculated
The calculator takes three measurements of a trapezoid: the lengths of its two parallel sides (the bases a and b) and the height h, which is the perpendicular distance between those parallel sides — not the length of the slanted edges. All three must be entered in the same unit; the area then comes out in that unit squared, while the midline is in the original unit.
It works by averaging the two bases, (a + b) / 2, which is the length of the midline (median). Because the trapezoid widens or narrows linearly from one base to the other, this average represents the trapezoid's effective width. Multiplying that average width by the height gives the area: Area = ½ × (a + b) × h, equivalently midline × h. This neatly turns an irregular four-sided shape into an equivalent rectangle of width midline and height h.
The formula assumes a flat, planar trapezoid with one pair of truly parallel sides; the angles and the lengths of the non-parallel (slanted) sides do not affect the area. All inputs must be positive, and results are rounded to four decimals, so irrational values are shown approximately.
Examples
| Input | Result |
|---|---|
| a = 8, b = 5, height = 4 | Area = 26, Midline = 6.5 |
About this calculator
A trapezoid (called a trapezium in British English) is a quadrilateral with exactly one pair of parallel sides, known as the bases. Its area equals the average of the two parallel sides multiplied by the perpendicular distance between them.
The midline, or median, is the segment connecting the midpoints of the non-parallel sides; its length is the average of the two bases, which is why the area can also be read as midline × height. This shape is common in roof cross-sections, embankments and land plots.
Frequently asked questions
Area = ½ × (a + b) × h, where a and b are the parallel sides and h is the perpendicular height between them.
A trapezoid has exactly one pair of parallel sides — these are the bases (a and b). The height is the perpendicular gap between them, not the slanted sides.
The midline is the average of the two parallel sides, (a + b) / 2. Multiplying it by the height also gives the area.
Also known as
TG we-Calculate Editorial Team. (2026). Trapezoid Area Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/trapezoid-calculator
TG we-Calculate Editorial Team. "Trapezoid Area Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/trapezoid-calculator.
TG we-Calculate Editorial Team, "Trapezoid Area Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/trapezoid-calculator
@misc{wecalculate_trapezoid_calculator, title = {Trapezoid Area Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/trapezoid-calculator}}, year = {2026}, note = {TG we-Calculate} }
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