Cloud seeding is considered a practical but unproved method to enhance precipitation or suppress hail, due to the insufficient knowledge of ice formation and evolution after seeding clouds with ice nucleating particles. This study investigates the aerosol size effects on the ice nucleation of commercial silver iodide (AgI) containing flares under cloud-seeding conditions. The generated aerosol exhibited comparable ice nucleation ability (INA) to pure AgI particles in the size range of 200 and 400 nm. Non-AgI impurities reduced the INA of flare particles <90 nm, which is higher when compared to pure AgI (< 40 nm). The critical mass ice-active site density of the generated aerosols (critical-nm) was derived based on our findings, indicating the minimum mass concentration of AgI particles required for efficient ice nucleation. The new parameterization to predict critical-nm can serve as a reference to optimize the effectiveness of cloud-seeding materials for practical use.