A computational strategy based on force-field calculations was developed to predict and analyze the packing in crystalline polymers. The strategy, which was incorporated in a computer program called Prediction of the Crystal Structure of Polymers (PCSP), takes advantage of the information provided by X-ray and/or electron diffraction. The program evaluates all the modes of packing for a given lattice dimensions, being able to predict the lowest energy one. The ability of the method to provide reliable results was proved by analyzing the crystal structure of four different polymers. Further, an insight on the applicability of the PCSP program to estimate the mechanical properties of polymers was provided by computing the elastic constants of the orthorhombic polyethylene.