A new model for concentration dependence of polymer chain dimensions over the wholeconcentration range was proposed. The hydrodynamic volume of a solvated macromoleculewas found to be a universal function of the degree of coil overlapping (c/c~*). The radiusof gyration (R_g) and the expansion coefficient (α) of polymer in solution or in bulk. pre-dicted by this model are much better in agreement with the experimental data of small angleX-ray scattering and neutron scattering from literature, than with the values predicted byother models and theories. A new model for concentration dependence of polymer chain dimensions over the wholeconcentration range was was proposed. The hydrodynamic volume of a solvated macromolecule was found to be a universal function of the degree of coil overlapping (c / c ~ *). The radius of gyration (R_g) and the expansion coefficient (α) of polymer in solution or in bulk. pre-dicted by this model are much better in agreement with the experimental data of small angle X-ray scattering and neutron scattering from literature, than with the values ​​predicted byother models and theories.