The modulus elasticity (or Young’s modulus) is considered to be a rather stable physical and mechanical characteristic of metallic materials being a weak function of the chemical composition and structure. However, the temperature and anisotropy can be referred as the main factors affecting the Young modulus. Scanty data on the scale factor effect on Young’s modulus are sometime even contradictory. We present the results of studying the impact of the scale factor on Young’s modulus of steel 45 determined by the tension of cylindrical tensile specimens with different initial diameters on an Instron 8801 machine with a movable traverse speed of 0.1 mm/min at room temperature. An extensometer and a digital image correlation (DIC) method were used to measure elastic deformations. Both methods showed fairly close results during tensile testing of specimens with equal diameters. DIC method made it possible to measure elastic deformations on small-size specimens on which it was impossible to fix the extensometer. A decrease in the Young modulus with an increase in the specimen diameter has been revealed. Graphical dependences of the Young modulus on the specimen diameter and cross-sectional area have been obtained. Possible reasons for the decrease in the Young modulus under the influence of the scale factor have been indicated. A decrease in the specific surface area and specific surface energy, an increase in the deformable volume, and a decrease in the strain rate at a constant movable traverse speed are among the main reasons. The decrease in Young’s modulus under the influence of the scale factor must be taken into account in strength calculations and in assessing the residual life of large-scale parts and structures with relatively large cross sections and wall thicknesses.