Based on kinetic considerations, the following equation, connecting the zero-shear viscosity of polymeric solutions with temperature and the molecular weight and concentration of the polymer was derived: RTln eta(R) = KBphiM(n)/(1 + BphiM(n)), where eta(R) is relative viscosity (Le., the ratio of the solution viscosity to the solvent viscosity); K represents a change in enthalpy of viscous flow from a pure solvent to a pure polymer at the same temperature or from a polymer of low molecular weight (M) to one of higher molecular weight, and has the dimensions of energy (e.g., J/mol) because the ratio BphiM(n)/(1 + BphiM(n)) is dimensionless; phi is the volume or molar fraction of a polymer in solution (concentration units can be used in dilute solutions); B is a constant related to the stiffness of the chains of the polymer in a given solvent; and at BphiM(n) much greater than 1, In 779 = K/RT. The equation describes published data on the zero-shear viscosity of four polar and nonpolar polymers in nine solvents with R-2 > 0.98. This approach allows the use of solutions of moderate concentrations for the characterization of polymers and opens a way for a single-point degree of polymerization (DP) determination of polymers at moderate concentrations if constants K, B, and n of the equation are known.