In this study, the degradation of cylindrical PMMA rods (diameter 20 mm) in a cone calorimeter is modeled by replicating the actual cross-section of the rods. The 2D heat transfer and pyrolysis algorithms of the Fire Dynamics Simulator (FDS) code are implemented to solve solid material degradation. Reaction kinetics were extracted from modeling TGA experiments of the PMMA sample under study. This novel framework allowed capturing time-resolved cross-sectional shrinkage upon a good agreement with experiments. Moreover, the method enabled the ability to extract more comprehensive thermodynamic information on the surface of rods such as heat fluxes and wall temperature distribution. The modeling procedure described in this work has the potential of further expansion to more complex cylindrical objects such as cables or thermal insulation materials, where charring, melting, and shrinkage processes are inherently multidimensional, and may determine the overall fire performance of the material or product.