This paper reports on the determination of the flame height of a flare system using theoretical approach based on the laws of conservation of mass, momentum and energy. The set of ordinary differential equations at steady state conditions are solved numerically by fourth order Runge-Kutta method. The extent of reaction between the fuel and the entrained air has been studied by introducing the reaction mixing efficiency parameter, as the reaction rate is fixed by local entrainment rate. The reaction mixing efficiency parameter is a key measure to determine the height of the flame and its variation with the source velocity is limited by the flame width and the maximum vertical flame velocity at the tip of the flaming region. The variation of different parameters as vertical flame velocity, flame geometry and flame temperature with flame height are shown in plots. It is found that the flame geometry undergoes an initial necking up to a certain height, followed by an increase in its spread thereafter. The flame geometry and the flame dynamics depend exclusively on the burner design and the stack exit velocity. The flame height to burner diameter ratio of the jet diffusion flame is found to vary linearly with Froude number with a constant slope in the logarithmic plot. © 2018 Universidad Nacional Autonoma de Mexico. All rights reserved.