A method has been developed to estimate the air leakage through high-use automatic doors. This air leakage is specified as a function of the rate of use of the door, the door geometry, and the pressure difference across the door. Two studies were carried out to obtain these results. One was a laboratory study of the discharge coefficients of doors of various geometries. The other was a field study of the times when automatic doors are open as a function of use. The results of the field study were analyzed and combined with the discharge coefficients that were measured in the laboratory study. The result was an air flow coefficient that is a function of the number of people using a door each hour. The designer can use this coefficient with the pressure difference across the door to estimate the rate of air leakage through the door.