Permeability of cement-based materials is the principal factor that provides its durability. Thus, several methodologies have been developed for measuring this property. Discrepancies in results can be generated due to large number of methods, mathematics equations and methodologies employed. Thenoz method is one method developed for measuring air permeability of porous media and have demonstrated good and satisfactory results, in accordance to several scientific researches. The aim of this work was to study the flow mechanism in a porous media, in particular a concrete media, evaluating Reynolds number and flow velocity of air outflow occurred when Thenoz method was employed to measure concrete air permeability. The Reynolds number results showed that outflow regime occurs in laminar form and validate the hypothesis to confirm the model. Tests were performed to verify the veracity of results obtained in accordance this methodology. Results have shown that air permeability measured by Thenoz method is a good test to evaluate concrete porosity.