The limit of perfection of a blast-furnace smelting, including in its concept a minimal theoretically possible coke consumption, is determined by a thermodynamic equilibrium of oxidation-reduction reactions in separate zones of a furnace. It is possible to determine minimum coke consumption, for example, with the use of the mathematical model suggested by us. The following prerequisites underlie the mathematical model. Heat exchange in a blast furnace was completed, i.e. there is a small thermal gradient between gas and charge on a certain height. In a certain zone of the furnace at a reduction stage of magnetite the reaction of wustite reduction tends to a thermodynamic equilibrium. In this zone so-called zonal reduction realizes when the processes of reduction of various iron oxides combine in time. The significant role belongs here to diffusion of gas in pores of iron ore material. The solution of equations set for the bottom zone presented by a condition of a thermodynamic equilibrium, namely, the equilibrium constant of wustite reduction by carbon oxide, material and thermal balances, supplemented by the equation of the heat balance for the top zone, allows calculating the main indices of blast furnace smelting. Indices thus calculated are extremely accessible (minimum) at the given parameters of charge and blast. In the paper quantitative values of the coke consumption were presented at stage and zonal reduction of iron oxides.