A simple approach to calculate rolling loads based on Sims' model was compared to a finite element model (FEM) using the same constitutive law and recrystallization equations. The comparison was done with a Nb microalloyed steel using a laboratory rolling simulation of plate and strip mill rolling schedules. The FEM model accurately predicted the temperature, the change in rolling loads, and the evolution of microstructure before and after transformation. These results clarified the accuracy of carious microstructure models, particularly the model for recrystallization. The FEM model gave an improved prediction of the rolling loads slightly compared with the slab method. For on-line modelling of the rolling loads a simpler approach based on Sims model gave acceptable prediction when using an accurate temperature model to predict the average temperature throughout the rolling process. The combination of the constitutive law and recrystallization kinetics in both cases enabled the prediction of the increase in rolling loads over the entire temperature range. The results also suggest that solute drag, rather than strain induced precipitation, has the primary effect on retarding recrystallization under the conditions examined.