GeomBench

Trapezoid Area Calculator

Average the parallel sides, multiply by height.

Parallel side a

Parallel side b

Height

Area

What you entered

Side a: 6Side b: 10Height: 4

1
Average the two parallel sides
(6 + 10) ÷ 2= 8
2
Multiply by the height
8 × 4= 32

Result

Area: 32

A trapezoid with parallel sides 6 and 10, and height 4, has an area of 32.

Trapezoid area from the two parallel sides and height

Area is the average of the two parallel sides multiplied by the perpendicular height between them.

Side a	Side b	Height	Area
4	6	3	15.00
5	9	4	28.00
6	10	5	40.00
8	12	6	60.00
10	16	8	104.00
12	20	10	160.00

Averaging the parallel sides first is what makes this work: a trapezoid with sides 6 and 10 has the same area as a rectangle 8 wide and the same height. That is a useful check on any answer. The height must be the perpendicular distance between the parallel sides, not the length of a sloping edge. If the two parallel sides are equal the shape is a parallelogram and the formula still holds, since the average of two equal numbers is the number itself.

The averaging trick

A trapezoid's area is the average of its two parallel sides, multiplied by the height between them — essentially treating it as a rectangle with an 'average' width.

Real-world trapezoids

Cross-sections of canals, roof trusses, and plots of land bounded by two roughly parallel edges are all commonly measured as trapezoids.

Frequently asked questions

How do I calculate the area of a trapezoid?

Area = ½ × (a + b) × h, where a and b are the two parallel sides and h is the perpendicular height between them. A trapezoid with parallel sides 8 and 12, height 5: Area = ½ × (8 + 12) × 5 = 50.

What is a trapezoid vs a trapezium?

In the US, a trapezoid has exactly one pair of parallel sides. In the UK, this shape is called a trapezium, while 'trapezoid' means no parallel sides at all. The formulas are the same — just the naming differs.

How do I find the height of a trapezoid?

Height = 2 × Area / (a + b). If you know a leg and the angle it makes with the base: height = leg × sin(angle). The height is always the perpendicular distance between the two parallel sides.