Flashover might occur rapidly as a consequence of non-accidental building fires. Response of the stored combustible items (being ignited and burned) should be studied carefully in such developed fires, which are ventilation-controlled. Air supply rate and heat fluxes acting at the materials would affect burning of the combustibles. A wide range of peak heat release rates with different fire durations results under different heat fluxes. The amount of combustibles denoted by fire or fuel load commonly adopted to quantify fire risks is no longer the key point in generating the heat release rate. A room with a large fire load may not give high heat release rates if the air supply is inadequate, or if the radiant heat flux is low. In this article, correlation of the peak heat release rate in burning the material under flashover with the fire load of the combustibles with adequate ventilation will be investigated. Data compiled from full-scale burning tests on well-developed room fires with steady burning are used to deduce a linear correlation between the possible peak heat release rate and the fire load density under adequate ventilation conditions.