Numerous research reports have demonstrated that the supply air volumes of cleanrooms areusuallyover-designed to satisfy air cleanliness classes, which may lead to enormous energy waste. In this study, five well-recognised international mathematical models for calculating cleanroom particle concentration wereanalysed, which are all based on uniform particle distribution in the cleanroom, indoor particle conservation, and mass airflow balance, and an improved and more general model has been established for calculating the minimum air change rates according to the expected air cleanliness class. Following the introduction of nondimensional concentration correction factors, based on the least-squares method, the average relative error between the model-predicted and measured particle concentration is approximately 13.5%. Based on the improved model with correction factor, the test results demonstrate that the particle concentration depends mainly on the air change rate, particle emission rate and return airflow patterns, among others. When the air change rate per hour and ratio of particle concentrations between the return airflow and room average were varied from 40 h^-1 to 120 h^-1 and 0.7–1.3, respectively, the concentration consequently decreased by approximately 65% and 46%. The particle deposition caused by gravity can be neglected for small particles