FIELD: measuring. SUBSTANCE: invention relates to the field of determining physicomechanical properties of materials. In order to determine the radius of curvature of the neck and the minimum diameter of a sample while stretching, the sample is subjected to a test while simultaneously recording the loading process. A digital photo or video camera is used for recording. Separate images of the sample with a neck are obtained, wherein the contours of the sample are accentuated and the coordinates of points belonging to the sample surface are determined. Based on the obtained values of coordinates, the longitudinal profile of the sample is approximated using a regression equation, wherein said equation is then used to calculate the radius of curvature of the neck and determine the minimum diameter of the sample. A part of the image within the initial working length of the sample is used herein to approximate the neck profile, and the neck profile is approximated using the corresponding equation. The values of the radius of curvature of the neck and the minimum diameter of the sample when stretching are then calculated. EFFECT: higher accuracy of the determined values of the radius of curvature of the neck and the minimum diameter of the sample due to the ensured high accuracy of approximating the longitudinal profile of the neck, irrespective of the size of the selected sample image area. 1 cl, 7 dwg.