The article presents the results of experimental studies that made it possible to substantiate the calculated dependences of the steam-cured concrete strength and the required values of the cement-water ratio (C/W) to ensure the specified strength values. For this purpose, dependences are obtained that are valid when using Portland cement and slag Portland cement, as well as a change in the wide range of regime parameters of heat treatment: temperature and duration of curing. To calculate the required values of C/W, a formula is justified, which allows determining the strength of cement under steaming when the temperature changes in the range of 60...95 С and the duration of isothermal heating during steaming from 4 to 18 hours. To calculate the strength of cement during steaming, the coefficients are recommended, which allow taking into account the content of aluminates and mineral additives in cement. Taking into account the calculated dependencies, an algorithm is proposed for calculating the C/W of steam-cured concrete and an example of its implementation.