From the basis of well-known molecular interaction potential equations, a model has been developed for calculating the micropore-size distribution of carbonaceous adsorbents from sub-critical adsorption equilibria of organic vapours. Only one simple iteration process and readily accessible physical properties are required for the calculation procedure. It is demonstrated that the resulting pore-size distributions computed from the characteristic curves of various sorbates agree well for a fixed sorbent. Thus, the model also allows the reliable prediction of the sub-critical adsorption equilibria of arbitrary organic vapours knowing the reference isotherm of another sorbate on the sorbent of interest. Even molecular sieve effects are reproduced; however, the assumption of spherical molecules only allows qualitative statements in respect of such effects.