The paper presents an original method to determine the 2D magnetic field in a square magnetic circuit. To do it, the method of Schwarz-Christoffel mapping is used. This mapping is a special kind of the conformal mappings, applicable to polygonal 2D configurations. As the magnetic circuit is complicated, a numerical solution has to be applied. Knowing the magnetic field, the fluxes and inductances are determined. The results are verified using FEM commercial software. © 2006 IMACS.