In gel permeation chromatographic (GPC) experiments of polymers

the quantitative relationship between elution volume and molecular weight

which is generally given by an empirical calibration equation

is very important. However

a clear theoretical derivation to this equation is absent in present polymer textbooks. This paper derives the two calibration equations widely used in experiments in terms of diffusion separation model and conformational entropy model

and gives the theoretical expressions for the phenomenological coefficients involved in the calibration equations. We further deduce the application range of the equations

which can be confirmed by literatures.