Losses in electrical machines for users are classified by IEC 34 in no load losses, load losses and additional losses. The latter are arbitrarily set to be 0.5% of the nominal power of the rotating electrical machine. This in fact is highhanded if is looked at the source of those losses. In this project a comparison of calculations of stray losses, the most important part of the additional losses, is given which is based on classical calculation schemes and on flux density calculations by finite element codes.