In this study a series of different molecular weight PEG solutions have been characterised for particle size and the results have been used, in conjunction with several other techhiques, to determine the pore size of the Nadir UH004 membrane. The resulting information, in conjunction with experimentally determined rejection profiles for the PEG solutions, has then been used to back calculate the hindrance factors for nanofiltration rejection theory. These experimentally derived values obtained for the hindrance factors were found to be in close agreement with the widely accepted theoretical predictions derived from hydrodynamic theory for micro and ultrafiltration. To our knowledge, this is the first experimental validation of these hindrance factors for nanofiltration and suggests that the correlations found throughout the literature are accurate enough for the calculation of hindrance factors describing the hydrodynamic drag forces experienced by a solute inside a nanopore. (C) 2015 Elsevier B.V. All rights reserved.