The paper presents the methodology for calculations based on the Newton’s method which was used to determine the characteristics of test unit injector systems. It allowed simplification of the research process by preserving a minimum number of measuring points and estimation of other data analytically. Results were compared with the real experimental results obtaining satisfactory accuracy of approximations. The proposed methodology was adapted to a standard spreadsheet so that changes in pre-set parameters and required computations could be made on a regular basis, which in addition shortened the time of their performance.