Trapezoid Area Calculator
Calculate the area of a trapezoid from its two parallel sides and its height.
Area
25
Area = ((a + b) ÷ 2) × height. Bases of 4 and 6 with height 5 cover 25 square units.
Average of the bases
5
How it works
A trapezoid has two parallel sides of different lengths, and its area is the average of those two sides multiplied by the height between them. Average the bases, multiply by the height, done.
That neat formula works because a trapezoid is, in effect, a rectangle whose width is the average of its two parallel sides. Seeing it that way makes the math feel obvious.
Enter the two parallel sides and the perpendicular height and the area appears instantly — useful for plots of land, roof sections, and plenty of everyday shapes that are not quite rectangles.
Frequently asked questions
How do you calculate the area of a trapezoid?
Add the two parallel sides, divide by two to get their average, then multiply by the perpendicular height between them.
Which sides are the bases?
The bases are the two parallel sides, whatever their length. The height is the straight-line distance between them, not the length of the slanted sides.
What if I only know the slanted sides?
You still need the perpendicular height for this formula. If you only have the slanted sides, you would need an angle or extra information to find the height first.