In order to develop a means to assess the effectiveness of some design elements for preventing upper floor tire spread, such as window geometry and arrangement of eaves above windows, possibility of scaling of window jet plume temperature distribution by means of a nondimensional temperature was explored. Experiments were conducted using two geometrically similar setups having different sizes to investigate the applicability of the nondimensional temperature to various conditions. It was found that the nondimensoinal temperature is independent of size and fire temperature but is uniquely determined only by geometrical conditions, that is, it is possible to predict real scale window jet plume temperatures based on the results of reduced scale experiments.