The purpose of this research is to focus on the solution of the resource sizing problem for the real production system. The resource sizing problem is tackled by usage of the mathematical makespan minimization method and comparative simulations of the two different production models. Only two production model simulations were realized due to specificities of the handled production system. Simulation results were presented, compared and discussed. This paper presents an approach which allows studying the heavy machine sizing problem realistically, through the use of simulation tools. The approach used would be of great help in making a decision on whether two new heavy machines should be introduced into an existing production system or not.