Prior knowledge of local increase in sheet metal thickness due to forming of products would contribute to decreasing total product weight by giving the product designer an advance notice of the appropriate sheet metal thickness distribution in a product. A method using simulation to accurately predict such increases would greatly aid the designer in this task. The designer can then distribute thicker parts where a large area moment of inertia is needed from the viewpoint of structural strength in a given section. In terms of optical designing for variable thickness distribution in products, the sheet thickness in a product need not be considered constant. This paper presents the forming prediction during deep drawing. To clarify the mechanism of increase in sheet thickness, a 3-D forming simulation is performed during deep drawing by using the finite element method (FEM). The effects of tool shapes—angle of contact with the original material and the contacting length of the punch with the material—that mainly affect the change in thickness of the original material are investigated. The thickness distribution of drawn cups is measured for comparing the simulation results obtained by FEM with the experimental results. It is shown that controlling the distribution of sheet metal thickness is possible if the original material is relatively thick, and when an appropriate manufacturing method is selected.