The dispersity of the dendrite crystals in steels is shown to depend on two factors, namely, kinetic (cooling rate) and thermodynamic (degree of dendrite coarsening) factors. The kinetic and thermodynamic solidification parameters that affect the dispersity of the dendritic structures in steels are studied. The quantitative contribution of each component to the well-known empirical formula that relates the distance between secondary dendrite arms to the cooling rate is determined. The division of this formula into thermodynamic and kinetic components opens up fresh opportunities for controlling the structure and properties of steels. The possibility of a concentration-induced or a thermodynamic change in the dispersity of the dendrite structure in steels is demonstrated.