Precise ventilation control of broiler houses is essential to effectively exhaust pollutants and attain the required breeding environment. However, the ventilation rate used in practise is always lower than the desired or designed value because of difficulties in measuring the pressure difference between the indoor and outdoor pressure of the facility. In this study, a new formula was developed to estimate the total ventilation rate for mechanically ventilated broiler houses using the number of operating fans and the slot opening rate, both of which are relatively easy to measure in practice. The proposed formula was derived from the in-situ fan performance curve and the discharge coefficient, which represent the ventilation characteristics of the exhaust fans and slot openings respectively. This was evaluated through a field experiment and a computational fluid dynamics (CFD) simulation. The measured ventilation rate was 24.1–26.6% lower than the desired ventilation rate showing that the in-situ fan performance curve was 33.7 Pa lower on average than the designed fan performance curve provided by the manufacturer. The distribution of static pressure in the broiler house was analysed using CFD models and it was found that the new formula could be applied to broiler houses having difference lengths.