Pressure swirl atomizers are widely applied in daily life and production activities. The spray angle is one of the most important parameters for the pressure swirl atomizers and mainly affects the spatial distribution of sprays and droplets. The quick prediction of the spray angle is important for the design and optimization of a pressure swirl atomizer. In the present study, the effects of length of swirl chamber, liquid viscosity and pressure differential on the hollow cone spray angle are studied by experiments. An available semi-empirical correlation for hollow cone spray angle prediction is derived by proper assumptions and simplification. This available correlation is validated by comparison with the experimental results. Besides, other correlations based on inviscid flow and viscous flow are also introduced to predict the spray angle for comparison. Based on the experimental results, the measured hollow cone spray angle decreases with the increasing of length of swirl chamber and liquid viscosity nonlinearly. The measured hollow cone spray angle shows no obvious growth with the increasing of the pressure differential when the pressure differential reaches a critical value. Further, the hollow cone spray angles predicted by the present available correlation agree well with the experimental results. The prediction uncertainties can be within ±15% for all cases. While, the prediction uncertainties are no less than ±40% by other correlations. Compared with previous correlations, the present available correlation can achieve better prediction accuracy. This available correlation is capable for the quick prediction of the viscous hollow cone spray angle.