This experimental study uses wind tunnel experiments to investigate the discharge coefficient and flow rate of wind-driven cross ventilation in partitioned buildings. The discharge coefficients of internal openings under different flow conditions were determined by a fan technique. It is found that the internal discharge coefficient is a function of internal porosity, but independent of external porosity and opening location. Based on the experimental results, a predictive model for the internal pressure of multi-room buildings is developed and verified. This model could be used to predict the flow rate through multi-room buildings once the external pressure distribution and opening areas are known.