In the paper, we make an attempt to estimate the size of informal economy on the base of micro-data. Two main approaches are described and compared. They are implemented on the base of an RLMS sample for 2012. The first method, called single equation approach, is based on the specific category of household expenditures and the arbitrarily defined household type (self-employed or employee). The second method allows to obtain the results for income under-report for both wage income and self-employment income, and uses information on all the household current consumption categories. The single equation model is restricted to one expenditure category and two types of households, although it enables to perform the estimation on different subsamples of households with various socioeconomic characteristics. The comparison of the system of equations approach with single equation is made concerning the scale of informal economy and the role of wage-income under-report, which is possible to obtain through the system.