Procedures for the determination of the log molecular weight vs. elution volume calibration relation are reviewed for linear homopolymers. The calibration curve is readily established with narrow molecular weight distribution fractions. For broad molecular weight distribution fractions the peak molecular weight at the peak elution volume of a fraction's gel permeation chromatogram has to be calculated from average molecular weights. When well-characterised fractions of the polymer requiring analysis are unavailable, a calibration curve can be established by procedures which assume that the hydrodynamic volume of a polymer molecule in solution controls fractionation in gel permeation chromatography. These universal calibration procedures require information on Mark-Houwink viscosity constants or polymer unperturbed dimensions. The validity of hydrodynamic volume as the universal calibration parameter is discussed with special reference to the goodness of the solvent for a polymer and polymer polarity. Examples are given of the various calibration procedures which are employed in the determination of molecular weight distribution and average molecular weights for poly(methylmethacrylate), polyethylene and polyisoprene.