Height requirement
The height must be perpendicular to the bases. A slanted side length is not the same input.
Example
With bases of 8 and 12 and a height of 5, the average base is 10. The area is 10 x 5 = 50 square units.
Common mistakes
Do not average all four sides. Only the two parallel bases are averaged. Also make sure the height is measured straight between the bases, not along a sloped side.
Limitations
This calculator assumes a standard trapezoid with two parallel bases. Irregular land or construction measurements may need a survey or a drawing split into simpler shapes.
Last reviewed: 2026-05-17