Reviewed by CalcMulti Editorial Team·Last updated: ·← Geometry Hub
A trapezoid (called trapezium in the UK) is a quadrilateral with exactly one pair of parallel sides. The area formula is A = ½ × (a + b) × h, where a and b are the lengths of the parallel sides and h is the perpendicular height between them.
This formula works by averaging the two parallel sides (giving an "average width") and multiplying by the height, just like a rectangle with that average width. This is why the formula simplifies to bh when both parallel sides are equal — which is a rectangle.
Common examples: drainage channels, cross-sections of embankments, roof truss panels, and many architectural shapes are trapezoidal.
A = ½ × (a + b) × h
Enter the two parallel sides and height. Add leg lengths for perimeter.
Optional: enter leg lengths for perimeter
½ × base × height — all triangle types
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This calculator is for educational purposes only and does not constitute professional advice. Results are based on standard mathematical formulas. Always verify critical calculations with a qualified professional before making important decisions.