Empirical rock mass classification systems are widely used in the practice of mining engineering, especially in the early stages of engineering design of mining infrastructure. This stage involves preliminary assessment of ground support needs for drifts and shafts, stability analysis of pillars and stopes, stability analysis of slopes in open pit mines, and others. During this preliminary stage of the design, mining engineers are required to consider different mining methods and mine designs, as well as underground and open pit alternatives. Crucial to design is the proper characterization of the rock mass, during and after the field data collection phase, in terms of available rock mass classification systems, such as Laubscher (MRMR), Bieniawski (RMR), Barton (Q) and Hoek & Marinos (GSI) systems. Because the rock mass characterization is normally done in terms of one (or rarely more than one) of these systems, and because different mechanical assessment tools used in this and later stages of mining design typically are expressed in any of the systems, it is important to be able to properly correlate rock mass classification ratings in the different rock mass classification systems. This process of correlating the ratings is not straight forward and has not been extensively treated in the literature. The aim of this paper is to address the problem of correlating rock mass classification information, and to propose new relationships for correlation of ratings, in particular, equations that allow to correlate the Laubscher and the Bieniawski systems, and the Barton and the Hoek Marinos systems.