Carbon dioxide in the supercritical state (sCO₂) has drawn much interest lately. It is considered as a promising fluid for next-gen power plants with many researchers investigating this technology. Cycle simulation and control requires compressor performance maps valid for variable inlet conditions. In this paper, an attempt is made for establishing a pressure ratio based performance map for sCO₂ compressors in power applications. For that purpose the so-called Glassman approach is considered. This model has been originally established for fluids obeying the ideal gas law. Therefore, a modification is proposed to take into consideration the real gas equation of state and to allow wide variation of the isentropic volume exponent k_v. Computational fluid dynamics (CFD) is used to predict the performance of a single stage radial compressor. Results for different k_vvalues at the compressor inlet confirms the validity of the proposed model with both the polytropic efficiency and the reduced enthalpy deviations limited to 1 percent. On the other hand, predicted pressure ratio shows difference of around 3 percent from k_v=7.1 to k_v= 4.1. A further decrease of k_v to 2.5 extends the difference up to 8 percent.