The area of a trapezoid is found by multiplying the average length of the two parallel bases by the height, or 1/2 (b1 + b2) x h. The height is the length of a line connecting one base to the other at a 90-degree angle.
A trapezoid is defined in the United States and Canada as a four-sided convex polygon with at least one pair of parallel sides. The same shape is called a trapezium outside of North America. In American and Canadian English, the word trapezium means a four-sided polygon with no parallel sides, also called an irregular quadrilateral. There is no simple formula for finding the volume of an irregular quadrilateral.