Torque influences the main phenomena that occur during friction stir welding (FSW) process. However, models for torque have received little attention. In this paper, inverse problem method is used to estimate the parameters for a model for torque, measured during FSW experiments for different combinations of rotational and welding speeds. The experimental results are used as input data to estimate the model parameters. The results showed a good agreement between the experimental data and the model obtained using the inverse problem method. The influence of the tool geometry on torque was observed by comparing previously published experimental results and the experimental data presented.