Downward sloping buoyant turbulent jet fires occur frequently during flammable gas leakage, while its flame trajectory, especially the quantitative length, is not well described. The flame trajectory lengths of downward jet fires with five sloping angles (0 degrees,15 degrees, 30 degrees, 45 degrees, 60 degrees relative to the horizontal) and two nozzle diameters (8 and 10 mm) were experimentally investigated. A novel method to quantify the flame trajectory length is proposed based on the flame outlines, and the results obtained show good agreement with the existing data of horizontal jet fires. For cases with differently inclined angles, the normalized flame trajectory length as a function of nozzle diameter can be correlated with the Froude number (Fr-1/5) and dimensionless heat release rate (Q*(2/5)), but not as function of the tilting angle as this is not considered in the existing correlations. In order to establish a global model for predicting the flame trajectory length of downward sloping jet fires as function of the tilting angle of the nozzle, a remodified Froude number (Fr-f*) is proposed, and the correlated result can describe all the current experimental results together with that of horizontal and vertically downward-oriented jet fires in the literature. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.