It is shown that the mass of the thermal blob, normalized by the mass of its effective monomer, is a unique function of the solvent quality represented by the Mark-Houwink-Sakurada exponent. This function specifies the relation between intrinsic viscosity and that measured in a theta solvent. As a result, the Mark-Houwink-Sakurada exponent can be determined from intrinsic viscosities measured for a single molecular mass. The form of the derived function is also confirmed by the constancy of calculated thermal blob mass for a given polymer of different molecular masses, dissolved in a solvent of a given quality. (C) 2009 Elsevier Ltd. All rights reserved.