  In the framework of the Gibbs statistical theory, the question of the size of
the particles forming the statistical system is investigated. This task is
relevant for a wide variety of applications. The distribution for particle
sizes and the moments of this quantity are determined from probabilistic
considerations. The results are compared with different models and
approximations. The particle size depends on the interactions in the system, on
the compressibility factor, on the number of interacting particles. The cases
of the absence and presence of a rigid incompressible particle core are
considered.
