A numerical investigation of the steam methane reforming process using RANS is presented. The effect of the geometric dimensionality of the reformer on the numerical results is investigated by performing CFD simulations with 1D, 2D and 3D computational domains. The commercial software ANSYS Fluent is used for this comparative analysis. The numerical study is performed for the wide range of the residence time and the relative length (radius/length). The comparison study of 1D, 2D and 3D models on steam methane reforming is performed for same CFD-code, initial conditions, catalyst type, approximation scheme, the convergence criteria, the turbulence model, the type of solution initialization. The results show the distributions of the mole fraction of the reformate products, temperature, methane conversion rate and diffusion flux inside a 150 mm length and 10 mm radius of steam methane reformer that is filled by nickel based catalyst. The differences between the results for 1D and 3D geometry become insignificant at the residence time of about 8 kg(cat)s/mol(CH4) and the relative length of 15. The difference between the results for 2D and 3D geometry is not significant as for 1D and 3D geometries. Almost similar results are achieved with residence time 4 kg(cat)s/mol(cH4) and relative length 15. Therefore, for engineering calculations of steam methane reforming, it is sufficient to use a 1D model if the residence time is more than 8 kg(cat)s/mol(CH4) and the relative length is more than 15. The 3D and 2D model should be used if the residence time and the relative length have a small value. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.