A simple method is devised for determining the effectiveness factors of spherical nickel catalyst pellets used for steam methane reforming (SMR) processes; specifically, the factors are determined for reforming conditions relevant to small-scale hydrogen production systems (1-3 bar pressure, 600-800 degrees C temperature, 2-4 steam/carbon ratio). The effectiveness factors are plotted with respect to a newly proposed effective Thiele modulus that considers the mass transfer limitation near the equilibrium methane conversion. Then, a modified Thiele modulus is introduced to make the effectiveness factors for various reforming conditions and structural parameters fall on a single correlation curve. The results indicate that the proposed method can properly describe the effectiveness factors of nickel catalyst pellets for the SMR conditions considered in this study. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.