In the present work, a model was proposed to simulate the growth in an industrial multi-chamber fluidized bed granulator under steady-state condition. To simulate the growth, it was assumed the coating is the only growth mechanism. Mass balance, as well as particle number balance (PNB), was considered in the simulation. Despite previous works, it was not assumed that particles in each chamber are at the same age. Consequently, the growth was simulated along the granulator length, from its beginning to the end. In this model, most of the influencing parameters are collected in one parameter called C-1. Using finite difference method, equations were solved and results were compared with samples from an industrial granulator and very good agreements were observed. Sensitivity of the product normalized mass density function to the parameter C-1 was also studied. It was found that for a specific inlet seeds diameter distribution, d(50) of the product is not a linear function of C-1. (C) 2020 Elsevier B.V. All rights reserved.