1. A method for estimating the volumetric capacity of an off-highway truck body design having a pair of side walls, a front wall and a floor, comprising the steps of: determining at least one material angle of repose of a heaped load to be carried by the truck body; establishing a three-dimensional model of the heaped load having a substantially conical upper surface that is based on the at least one material angle of repose and that intersects portions of the side walls, front wall and floor of the truck body design; and calculating a volume of the three-dimensional model of the heaped load.