The aim of the present study was to propose two ways for calculating the final price to be paid to suppliers of forest biomass based on the energy content of the fuel. Moisture content (MC) and ash content (AC) were considered quality indicators for a co-generation plant located in Lages, state of Santa Catarina, Brazil. Two models are proposed for the three biofiiels most acquired by the plant (wood chips, sawdust and bark): Model 1, based on the Net Calorific Value (NCV) estimated considering the moisture content (MC) and ash content (AC) of the biomass; and Model 2, with the AC discounted from the dry weight of the biomass and subsequent estimate of the NCV considering the MC. The final price corresponded to the calculation between the weight and estimated NCV, with the suggestion of a bonus and discount for materials of better or worse quality, respectively. A significant reduction in biomass weight occurred after the ash discount, especially in the case of bark, which had a high AC. The price paid for kJ of biomass proved to be more coherent than the price per ton, since the ash and water content of the material is taken into account.