The challenges associated with biofuel quality come from its heterogenous nature as biomass crops grow in different lands and under different conditions. Moreover, the inconsistency of the handling and sampling techniques in the laboratories or in the feedstock storage piles increase biomass variability. These issues affect the calorific value and as a result, the accuracy of the measurement for each feedstock pile of the measured data might be widely scattered. Furthermore, the current standards, e.g., ISO, DIN or ASTM are limited and do not consider the deviations caused by determination errors during the measurements. Therefore, this study quantifies the causes of these deviations by performing an inter-laboratory comparison on a metrological level between 3 national metrology institutes. Eventually this comparison helps to optimize the existing strategies and provides an enhanced technical practice for the determination of the calorific value by bomb calorimetry. It has been found that by assuring that the equilibrium moisture content of the samples is reached and that by avoiding the sources of error during the measurements, the repeatability of the samples can be improved by up to 50%. Consequently, this improvement will help to lower the final uncertainty by 10-25%.