Recently, there have been prerequisites for expanding the scope of application of formalized models in the social sciences and humanities, but the problem of measurability or quantitative assessment of many concepts in social sciences and humanities is still poorly understood. The purpose of this article is to formulate general principles of integrated assessment, which would be distinguished by the use of an objective approach when creating measurement procedures in relation to the states of complex systems. It is assumed that on the basis of the selected measures of similarity, it is possible to construct a measurement scale for comparing states with each other. The main measurement principles used are the law of corresponding states and the two-point method, which consists in constructing a linear reference process on two states of the reference object. In the proposed method, the main object of measurement and modeling is the state of the system, which is determined, on the one hand, by properties, and, on the other hand, by complex measures related to the entire group of observed objects as a whole. This makes it possible to establish the relationship between the parameters of the properties of objects in the form of equations of state, for which, on the basis of the selected measures of similarity, a measuring scale is constructed for the relative comparison of states with each other. Using specific examples for socio-economic and natural-anthropogenic systems, the process of developing such procedures, which differ in the use of an objective approach to measurements, is illustrated. The use of geometric, probabilistic and empirical measures of similarity in measuring the states of complex systems is demonstrated. In general, the proposed approach can be used for complex measurements in both socio-economic and humanitarian sciences.