Accurate knowledge of an adsorbent's porosity is of fundamental importance for scientific and industrial application. Despite using highly sophisticated physical models, all current approaches make assumptions resulting in significant differences in pore size distributions depending on the modeling parameters used. The molecular probe method presented in this paper applies a minimum of approximations. Differences in pore volume can be reduced to sterical limitations in micropores below the size of adsorptive, leading to a high-resolution pore size distribution below 0.7nm where only few comparable methods exist.