A modification of the method for calculating the distribution function of random fields of dipole-dipole interaction in dilute magnetics using the expansion in the Gram-Charlier series with the help of Bell polynomials has been carried out. On the basis of this method, a model has been developed that allows us to estimate the ensemble magnetisation, the volume fractions of particles in different magnetic states, the volume concentration of the ferrimagnetic and its effective spontaneous magnetisations on the basis of experimental data on hysteresis characteristics. The proposed approach allows us to take into account the particle size distribution and magnetic states. The model has several advantages, such as the possibility of taking into account the cluster distribution of particles and applicability to the limiting cases of thin layer and thin filament. Examples of partial verification of this model on objects of artificial and natural origin are given.