Trapezoid Area Calculator
Enter the two parallel sides, height, and the two slanted sides to calculate a trapezoid's area and perimeter.
Last updated: September 5, 2026
Frequently asked questions
What is the formula for the area of a trapezoid?
Area = ((a + b) / 2) × h, where a and b are the lengths of the two parallel sides and h is the perpendicular height between them.
What is the area of a trapezoid with parallel sides 6 and 10 and height 4?
32 - ((6 + 10) / 2) × 4 = 8 × 4 = 32.
Why do I need all four sides to find the perimeter, but only the parallel sides and height for the area?
Area only depends on the two parallel sides and the distance between them, but perimeter is simply the sum of all four side lengths - including the two non-parallel (slanted) sides, which don't factor into the area formula at all.
Is a parallelogram a special case of a trapezoid?
Yes, under the inclusive definition most math courses use - a parallelogram is a trapezoid where both pairs of opposite sides are parallel. Some definitions exclude parallelograms, but the area formula works either way since it only requires knowing one pair of parallel sides.
What if I only know three sides and the height, not both parallel sides?
This calculator needs both parallel sides (a and b) and the height to compute area - if you're missing one parallel side, you'll need another known angle or the slanted side lengths together with trigonometry to solve for it first.
How do I find the perimeter of a trapezoid?
Add up all four sides: perimeter = a + b + c + d, where c and d are the two non-parallel (slanted) sides - enter them in the optional fields to get the perimeter alongside the area.
Is a trapezoid the same shape as what's called a 'trapezium'?
It depends on the country - in American English, 'trapezoid' means a quadrilateral with exactly one pair of parallel sides, which is what British English calls a 'trapezium.' Confusingly, British English uses 'trapezoid' for a quadrilateral with no parallel sides at all.