How to Use the Trapezoid Area Calculator

Enter both parallel bases (base a and base b) and the perpendicular height between them.

area = ½ × (base a + base b) × height

Averaging the two bases before multiplying by height is what separates this from a plain rectangle or parallelogram formula — a trapezoid's two parallel sides are different lengths by definition, so the shape's width effectively changes from one end to the other, and the average is the width that would give the same area as a rectangle.