Abstract The heat feedback profile across 5cm wide and 15cm tall samples of poly(methyl methacrylate) was studied from ignition until total sample involvement as a flame spread vertically upward. Incident heat flux to a water-cooled gauge was measured at 1cm intervals. At 6–15cm above the bottom edge of the flame, the maximum heat flux value was found to be on the order of 35kWm−2. Lower in the sample, 2–5cm above the flame bottom, where the flame is thinner and thus closer to the sample’s surface, the maximum heat flux is slightly higher, about 40kWm−2. Using these results and finely resolved measurements of sample burning rate recorded throughout the length of experiments, an analytical model that accurately predicts the measured heat flux profile along the vertical dimension of samples solely as a function of the burning rate was developed. Coupling this model with an accurate pyrolysis solver, which predicts material burning rate based on incident heat flux, is expected to enable highly accurate simulations of the flame spread dynamics.