This study is an investigation of the accuracy of reconstruction techniques for determining instantaneous fuel regression rate. Results of reconstruction techniques are compared with results obtained through the measurement of the pressure drop across the fuel in an Axial-Injection End-Burning hybrid rocket (EBHR). The results of numerous firing tests show that this method allows for the evaluation of the accuracy of the instantaneous fuel regression rates obtained by reconstruction techniques. The error bias of O/F values calculated by the reconstruction techniques were around ±10%, and were mainly caused by uncertainties in the measured values of oxidizer mass flowrate and the definition of firing duration. The instantaneous length of an EBHR-type fuel can be calculated from the measurement of the pressure drop across the fuel. However, the calculated fuel length history obtained by the pressure drop in a port does not coincide with that obtained by the reconstruction technique because of an underestimation in pressure drop.