In conventional studies, different empirical atomization equations are correlated for different kinds of atomization methods or even in the same method. In the present study, it was found that the basic law of melt breakup from bulky liquid into droplets can be universally applied to all atomization methods. Based on theoretical analysis, a new general equation of mean particle size applicable to both conventional atomization methods and new atomization processes is presented. The mean particle size in melt atomization is mainly controlled and decided by two key dimensionless parameter groups representing the liquid stability of melts and the breakup ability of atomizer respectively. Different specific atomization mechanisms result in different formulae in conventional atomization methods. In case of gas atomization, it is equivalent with and can be changed into Lubanska Equation. In case of centrifugal atomization, it can be changed into the equations that are currently the most widely used. In case of water atomization, it is similar to the equation proposed by Grandzol and Tallmadge. According to the universal equation, new correlations for mean particle size in novel atomization processes such as Hybrid Atomization and Multistage Atomization were proposed and agreed with our experimental data well.