Centrifugal compressors are used in automotive, aerospace, industrial equipment, air conditioning, petrochemical and many other sectors. Although the sectors they are used in are different, the common purpose of them is to increase the pressure of the flow and they are of critical importance for the continuity and performance of the systems in which they are used. Optimal design of centrifugal compressors in accordance with the requirements of the system in which they are used will increase the efficiency of these systems. This study deals with the efficacious use of computational methods to create optimal centrifugal compressor designs for given input parameters. The present process has four steps: preliminary sizing, throughflow analysis, Computational Fluid Dynamics (CFD) analysis, and optimization. In the preliminary sizing step, gas dynamics and Euler turbomachinery equations are used to calculate the basic dimensions of the impeller and the volute. The preliminary sizing algorithm presented in this study differs from the sizing algorithms of the existing turbomachinery design tools as it does not require the design point rotational speed value from the user. The basic dimensions that obtained by the preliminary sizing algorithm are then used to create the parametric 3D geometries of the impeller and the volute in a turbomachinery specific Computer-Aided Engineering (CAD) tool. In the throughflow analysis step, analyses generate the 2D flow results using the meridional geometry from the created parametric impeller and volute geometries. The throughflow analyses results are used in a genetic algorithm (GA) based optimization study to obtain the optimal impeller geometry that gives the maximum rotor efficiency. In the final step, a CFD model including the optimal impeller and the parametric volute geometry is created. The optimal volute geometry that leads to minimum total pressure loss is obtained by a GA based optimization using the CFD analyses. The CFD results' validity are checked against a reference centrifugal compressor's test results. This study also indicates that preliminary sizing followed by a well-built throughflow analysis eliminates the need for a fully parametric 3D CFD-based rotor design.