Cyclones are the most commonly used air pollution abatement device for separating particulate matter (PM) from air streams in agricultural processes, such as cotton gins. Several mathematical models have been proposed to predict the performance of cyclones as cyclone diameter varies. The objective of this research was to determine the relationship between cyclone diameter and cyclone cut point based on empirical data. Tests were performed comparing the cut points of 6-, 12-, 24-, and 36-in. diameter cyclones with poly-disperse PM having an aerodynamic mass median diameter near 10 ìm. The mass and particle size distribution of PM collected by the cyclones and that which penetrated the cyclones was used to determine the cut point of each cyclone.