As molten corium is ejected from a reactor pressure vessel (RPV), the melt undergoes fuel-coolant interaction (FCI). Through the FCI molten corium is fragmented into small particles, and the fragments will form a debris bed stacking on the bottom of the cavity. Heat removal performance from both fragments and the debris bed is highly related to the size of fragments. Also, as FCI is a thermal-hydraulic interaction on the interface between the corium and the coolant, the estimation of the Sauter mean diameter is required. Thus, in this study, we develop a simplified strategy to predict the Sauter mean diameter with particle size distribution. The model is proposed to calculate the particle size distribution based on upper-limit log-normal distribution and the critical Weber number criterion. The calculation results are compared with 9 cases of FARO experiments and 7 cases of TROI experiments. The particle size distribution calculated with the suggested method well follows the trend of measured distribution from experiments. The estimated Sauter mean diameter varies from 1.58 mm to 3.13 mm, while the results for the ratio of the mass mean diameter to the Sauter mean diameter is almost constant to 1.55. It turns out that the suggested model gives good predictions of the particle size distribution and the Sauter mean diameter without large computational effort.