The effective thickness of absorption multiplex holograms are evaluated by a numerical analysis of angular-selectivity curves obtained by the reconstruction process. These transmission holograms were respectively recorded in sequential and incoherent superposition of 2, 10, or 21 volume-coupled gratings. The experimental effective thickness represents 50% of the nominal thickness associated with Kodak 649F plates for 21 recorded, coupled gratings. The many experimental unpublished curves presented in this paper for 10 and 21 gratings permit one to obtain interesting numerical values of the thickness and angular-selectivity bandwidth of resultant multiplex holograms.