The paper shows that a planetary magnetic field expressed in the conventional form of a spherical harmonic expanson can be completely represented by the vector sum of fields produced by a set of magnetic dipoles with different magnetic moments, tilted from the planetary spin axis and offset from the planetary centre by different amounts. For convenience, the transformation from multipole systems to dipole systems is restricted to that from multipoles up to octupole to five dipoles. The scalar equipotential transformation analytically results in 24 equations; these can be subsequently solved for the 24 adjustable parameters in dipole systems with the predetermined `main dipole'. The numerical comparison of the jovian magnetic field between the jovian O$_4$ and the five-dipole models reveals a very good agreement with the subtle details. It is obvious that this type of transformation would open up the simplest practical way to simulate planetary magnetic fields with the dipole patterns.