Abstract: The object of study involves the method for assessing the quality of technical interoperability means in the open information systems in accordance with the model of interoperability under the GOST R 55062-2012. The author proposes a method for calculating the estimated characteristics of technical interoperability based upon the evaluation of detection and transformation of data formats by nodes of an open information system. As an example the article includes practical assessments of technical interoperability based upon the criteria for detecting and converting formats, and some software packages for processing graphic images. It is noted in the article that if there is need to observe the evolution of the interoperability of the information system, it is then necessary to preserve the methodological basis for the formation of the initial parameters. The proposed estimation method is based upon the laws of information theory and it is determined by a formal model allowing to calculate the particular and general information entropy characterizing the technical interoperability as the ability of the information system under investigation to detect data in various formats and the ability of the information system under investigation to produce correct data transformations in various formats. The main result of the research is the developed method of estimating technical interoperability that allows to make a numerical estimation of the properties of technical interoperability allowing for the format detection and transformation. The practical result of the study is that it enables the numerical evaluation of interoperability, allowing one to monitor the dynamics of interoperability of various systems under conditions of interaction with a continuously changing inter-system information space.