The saturation magnetization of single-crystalline garnet ferrite films of different compositions is calculated on the basis of the familiar relations of the Neel model on the sublattice structure of ferrimagnetic compounds. Other parameters of the films are calculated using the theory of strip domains and the stability theory of cylindrical magnetic domains. The presented material is educational and intended for use in practical exercises in the study of magnetism. The problem is given to students of specialties 22.03.01, Materials Science and Materials Technology (when studying the discipline of Physics of Magnetic Materials); 03.03.02, Physics (when studying the disciplines of General Physics, in the section on Electricity and Magnetism and the disciplines of the Magnetic Properties of Matter); and to students of specialty 13.03.02, Electric Power Engineering and Electrical Engineering (when studying the discipline of Magnetic Measurements) at Astrakhan State University.