Almost all properties of hydrated cementitious materials depend strongly on their pore structure. Many methods to quantify porosity have been applied to cementitious materials, but there is a huge confusion in the literature about the utility of these methods. By comparing the results between different methods, including MIP, 1H NMR and nitrogen adsorption, we highlight that semi-quantitative information can reliably be obtained from these methods. In particular, we demonstrate that they are consistent in their relative range of validity. This range of validity is explained in terms of microstructure features. We also show how the results are linked to macroscopic observables such as microstructure development (degree of hydration) and transport (conductivity and apparent chloride diffusion).