It is often necessary to calculate the stress strain state of reiforced concrete members at normal sections. The calculations have to be performed at different stages of loading: before cracking, at the cracking moment, in sec-tions on the crack under service and breaking load.For the calculations, very inaccurate diagrams of the stresses are used. There is no possibility to calculate height of the cracks and height of tensile zones of the con-crete above them. The height of compressive zone of the concrete is especially inaccurate. It is impossible to calcu-late the mentionned parameters for the stages before crack-ing and before fracture. It is impossible to define these parameters in plastic hinges of the continuity beams. There is no method of stress strain state calculation of reinforced concrete members according to the measured parameters of normal cracks (height and width of the cracks and distance between the cracks) in stages close to fracture load.It is possible to solve many of these problems us-ing more realistic curvilinear diagrams of interrelation be-tween strain and stress of concrete. But its use is aggravat-ed by the integration problem.The author of the article offers his equation for the calculation of normal stress of heavy and fine-grained concrete of strength classes C8/10-90/105. It is resonable to use this equation in cases when there is a need to inte-grate the curvilinear diagram of the stress when making equations of the static equilibrium of stresses.