Trapezoid Calculator

About this calculator

A trapezoid has exactly one pair of parallel sides, called the bases (a and b), and its area follows directly from averaging those two bases and multiplying by the height between them: Area = ((a + b) / 2) × h — essentially treating the trapezoid as a rectangle with the "average width" of its two parallel sides. The perimeter simply adds the two bases to the two non-parallel legs.

This shape and formula appear constantly in land surveying and civil engineering, where irregular plots and cross-sections of roads, canals, and retaining walls are frequently trapezoidal; surveyors compute areas of trapezoidal land parcels this way, and hydraulic engineers use the same formula for trapezoidal channel cross-sections in irrigation and drainage design.

Architects sketching roof sections, carpenters cutting trapezoidal panels, and geometry students all rely on this formula because it turns an irregular quadrilateral into a calculation as simple as a rectangle's, once the two parallel sides and the height are known.