Charge-carrier transport in an energetically and spatially disordered hopping system is analysed in terms of dimensionless distance and energy variables. The transport characteristics are shown to be described by three dimensionless parameters which in essence represent the concentration, temperature and electric field respectively. Consequently, a relationship is predicted between these parameters and certain scaling properties of the curves of mobility against field and mobility against temperature. This is supported by mobility measurements carried out on a hole transporting compound doped into polycarbonate within the widest concentration range reported so far in the literature.