This document defines and provides area formulas for common quadrilaterals: trapezoids have one set of parallel sides and two congruent angles; parallelograms have opposite sides that are congruent and parallel; rectangles have two sets of parallel sides and right angles; rhombuses have four equal sides; and squares have equal sides and right angles. The area formulas provided are: for rectangles, length times width; for squares, the length of a side squared; for parallelograms, base times height; and for trapezoids, the average of the top and bottom bases times the height.