Preliminary staging studies of multi-stage space launchers are described. Both propellant and thrust scaling factors are used, and also cost parameters for propellant, propellant scaling units and thrust scaling units. The general minimum cost study, including reusable stage(s), turns out to be a generalisation of the optimisation method of the payload ratio, for specified mission requirement. Both studies lead to a velocity increment distribution between the stages, based upon optimum initial acceleration for each stage. The similarity between this analysis and that developed by Vertregt, Hall and Zambelli, and others is pointed out. Penalties for non-optimum solutions are also considered.