Trapezoid Area Calculator
Area from the two parallel sides and the height between them.
The formula
area = (a + b) / 2 × h
Average the two parallel sides, multiply by the height. It works because a trapezoid is exactly a rectangle whose width is that average. Sides 10 and 6 with height 4: (10+6)/2 × 4 = 32.
Height, not leg
The h in the formula is the perpendicular distance between the parallel sides, not the length of a slanted leg. Using the leg overestimates the area; on a nearly-right trapezoid the difference is small, on a low, wide one it's huge.