In this paper, a methodology has been proposed according to which, after carrying out a set of soil's resistivity measurements, one can compute the parameters of the multilayer earth structure using a genetic algorithm (GA). The results provided by the GA constitute the indispensable data that can be used in circuital or field simulations of grounding systems. The methodology, developed on the base of the PC Opera software package, allows to proceed toward a very efficient simulation of the grounding system and an accurate calculation of potential on the ground's surface.