**The surface area of a trapezoid is calculated using the equation 1/2(a+b)*h, where "a" and "b" are the parallel sides of the trapezoid, and "h" is the vertical height.** For example, if side "a" equals three, side "b" equals five and height "h" equals four, then the area equals 1/2(3+5)*4, or 16.

A trapezoid is a type of two-dimensional shape known as a quadrilateral. As with all quadrilaterals, a trapezoid has four sides. Trapezoids have one set of parallel sides. These sides are known as the bases of the trapezoid, while the two non-parallel sides are called the legs. The vertical height is also known as the altitude. When the legs are equal in length, and the angles from a parallel side are equal, the shape is an isosceles trapezoid.