A new flow metering system using an ultrasonic Doppler method has been developed. By this method, an instantaneous velocity profile is measured and its integral is evaluated to give flow rate. Instead of making multidimensional flow mapping to evaluate its performance, the method was assessed in laboratory experiments where single line measurements were used over the whole pipe diameter or radius to determine the flow rate. The system shows a good capability of tracking transient flows. Its accuracy was investigated using the National Institute of Standards and Technology (NIST) flow standards in Gaithersburg, MD, USA; averaged results show its deviation from NIST results to be 0.18% for Re=400K and 0.58% for Re=2.6M. Good repeatability and reproducibility were also confirmed.