An exemplary method for determining a flow rate of a pump, includes measuring and storing the flow rate (QMean) when the pump is in operation, storing rotational speed (nMean) and torque (TMean) of the pump during measurement of the flow rate (QMean), determining torque (TManufacturer) corresponding to the measured flow rate (QMean), calculating a bias value of the torque (TBias) by comparing the torque determined from the characteristic curve (TManufacturer) and the stored torque (TMean) of the pump, and determining an operating point of the pump based on the bias value of the torque (TBias).