This article proposes a Blade Element Momentum (BEM) theory based model applied to dual rotors wind turbines. Dual rotor wind turbines studied consist of two rotors mounted coaxially to recover the flow from the first rotor. These rotors can turn in the same (co-rotating) or in opposite directions (counter-rotating). The aim of the model is to be fast, accurate and configurable in order to be used as design tool or for optimization purposes. The model considers axial and tangential induction influences of the first rotor on the second one and the influence of the distance between them. The model has been validated by comparison with experimental data from the literature and shows that the counter-rotating configuration has a power coefficient 4.6 % higher than the co-rotating for the same turbine geometrical setting. Besides, in our case study, the counter-rotating power coefficient can be in average on different wind speeds 10.6 % higher compare to the single rotor.