The influences of main dimensions and operating conditions of simplex swirl atomizers on the thickness of the annular liquid film formed at the discharge orifice are examined. A general expression for film thickness is derived which, when compared with the experimental measurements reported in the literature, shows very satisfactory agreement over wide ranges of atomizer dimensions and liquid injection pressures. When measured values of Sauter mean diameter (SMD) are plotted against the corresponding values of liquid film thickness t, a relationship between SMD and t is obtained which corresponds closely to the results of previous studies on both airblast and simplex atomizers. The analysis also leads to the development of correlations for flow number and discharge coefficient in terms of the main nozzle dimensions. Predictions of flow number and discharge coefficient based on these equations show satisfactory agreement with the experimental results reported in the literature.