Trapezoid Area (Parallel Sides) Calculator
Find the area of a trapezoid from its two parallel sides and the height between them using A = ½ (a + b) × h.
How it works
A = ½ · (a + b) · h · where a, b = parallel sides, h = height between them
A trapezoid’s area is its average width times its height. The average of the two parallel sides — called the midsegment — is the width halfway up, and multiplying it by the perpendicular height gives the area. The two slanted (non-parallel) sides never enter the formula; only the parallel sides and the distance between them matter.
Worked example
For parallel sides of 8 and 12 units with a height of 5 units, the midsegment is (8 + 12)/2 = 10, so A = 10 · 5 = 50 square units.
Sources: Trapezoid — Wikipedia
Frequently asked questions
Do the slanted sides affect the area?
No. Only the two parallel sides and the perpendicular height between them determine the area. Different slanted sides can give the same area as long as the parallel sides and height are unchanged.
What is the midsegment?
The midsegment is the line halfway between the two parallel sides; its length is the average of them, ½(a + b). Multiplying it by the height gives the area directly.
What if the two parallel sides are equal?
Then the shape is a parallelogram and the formula reduces to A = a · h, the standard parallelogram area.
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This calculator is for educational purposes. Double-check important results before acting on them.