Abstract A new calibration method of flow meters for a divided flow humidity generator is proposed. Such a generator usually has two flow meters, one for measuring air flow of the saturator and the other for measuring dry air flow for dilution. The proposed method is to introduce a third flow meter for the measurement of total flow, and by comparing the readings of these three flow meters, instrumental errors of the three flow meters are obtained by least squares calculation. The validity of the method is confirmed by calibrating the flow meters with a flow calibration system using sonic nozzles. The measured characteristics of the flow meters and the correction of humidity value of the generator are described.