A theoretical model for the shape of a planar laminar jet diffusion flame in the buoyancy- controlled regime has been developed and the results of a comparison between the theoretical results and previously reported experimental data are presented. The two-dimensional flame shape model is based on an extension of the classical buoyancy-controlled flame height model of Roper. The derivation of the model is presented along with the simplifying assumptions. In the buoyancy-controlled regime, the flame height is known to be a function of the gravitational acceleration and, thus, the theoretical results are compared to experimental data at different gravitational levels. Despite its simplicity, results from the model showed good agreement with the experimental data. By employing a simplified description of flame behavior, a more tractable representation of the physical transport mechanisms responsible for the experimentally observed behavior is obtained.