Contravening building construction rules, using low-quality materials and lack of precise knowledge of the building structure are some of the reasons for the structure's failure during an earthquake. Given the pervasive use of steel structures in Iran due to its advantages, it is necessary to carry out thorough studies in design, construction, and maintenance of steel structures to establish a reliable, accurate and optimal standard. Girders are one of the most commonly used steel structures. Girders are used in many types of structures such as bridges, niches, buildings and so on. One of the issues that seem to be important in the manufacture of girders is its tolerance. There is a wide scope of the steel tolerance debate that can be seen in different parts such as bolt tolerance, welding tolerance, and dimensional tolerance, etc., and the impact of any type of tolerance is inevitable. Section 10 of the National Building Regulations of Iran, entitled "Design and Implementation of Steel Buildings," discusses tolerance in its fourth section. While one type of tolerance cannot be considered more important than the other, two types of welding and dimensional tolerance are among the most common types of tolerance, and many problems can arise by ignoring these two tolerances in the steel structures design. In the foregoing study, the discussion of dimensional tolerance and more precisely Section 10-6-6-3-7 in the 10th section will be discussed. This thesis, which numerically addresses the impact of tolerance on the steel flange and webs of steel plates using ABAQUS software, illustrates the effect of flanges and/or webs rotation on bending strength of the steel girder. In this research, we have investigated the combination of 2 web plate specimens and 3 flange plate specimens which results in 5 steel girder models, all of which are 1.8 m long. Each of these five models has 4 tolerance samples, which can be said to be 215 in total. Flange plates were 2, 1.5 and 1 cm thick