Scientific research of the concept and essence of the middle class, criteria for its identification, social, economic and other characteristics of this class are relevant both for theory and practice. Substantiation of issues related to the definition and peculiarities of the formation of the middle class requires in-depth research of specialists from different research areas, and first of all specialists in the field of quantitative and qualitative methods of evaluation and analysis of the middle class who are engaged in the development of models, in particular models of distribution of elements of the society (households) according to indicators of welfare (income, liquid savings, wealth in general). In this regard, the purpose of this research is to generalize the formalization of the middle class with the help of the Lorentz function and to establish a priori estimates of the uneven distribution of the total wealth or other indicator of well-being (income, liquid savings, etc.) in the society, depending on the parameters of the middle class. The article reveals the essence of the middle class as a fundamentally important layer of the society, which has a certain (different for different societies) share of social wealth (income, liquid savings, wealth in general, etc.). The middle class is formalized with a set of parameters that identifies two points of Lorentz curve characteristic for the research society. There were established the double-ended estimate for the Gini and Robin Hood coefficients, which functionally depend on the parameters of the middle class and can be used both for the evaluation of other characteristics of the uneven distribution of social wealth, as well as for other tasks of quantitative and qualitative analysis of socio-economic structuring of the society.