This paper focuses on the uncertainty associated with the heat release rate calculation for the cone calorimeter. The component uncertainties of the simplifying assumptions and experimental measurements are quantified in order to assess the overall uncertainty of heat release rate calculations, but random uncertainties associated with the sample and operator errors are not considered. An example is presented that shows how the individual component uncertainties propagate through calculation. It is clear that the greatest component uncertainties are attributed to the assumed combustion expansion factor, assumed effective heat of combustion, and the measured oxygen concentration. Having examined the component uncertainties, several strategies for reducing overall uncertainty are proposed.