This contribution deals with a numerical solution of a centrifugal impeller's prime geometry. A numerical description of impeller's geometry is transformed into a 3D CAD software. The numerical solution is based on a one dimensional theory with a correction to a finite blade count. The proposed prime geometry is supposed to be tested through a CFD simulation. The aim of the CFD simulation is to optimize the prime geometry of a pump. The numerical solution of the prime geometry varies according to specific speeds and a shape of the impeller's main streamline. An interface between the numerical solution and 3D CAD program is provided by a text document. Some examples of impellers with different specific speeds are being shown in the paper.