Dense metal membranes have been tested for evaluating their hydrogen permeability. Two experimental procedures have been employed in order to measure a large range of hydrogen permeation fluxes: dynamic and static tests. The second procedure has been applied to membranes characterized by very low hydrogen permeability: it requires the exact knowledge of the volume of the experimental apparatus. A mathematical model has been developed for establishing the relationship which exists between the membrane permeance, the volume of the apparatus and its internal pressure. Based on this experience, a new method has been established to determine the volume of both gastight and non-gastight vessels by using porous membranes of known permeance operating with air or other gases. (c) 2006 Elsevier B.V. All rights reserved.