An ultrasonic flow meter system includes a conduit defining a channel, at least one pair of first transducers, at least one second transducer, and a processor. The pair of first transducers is mounted on the conduit and includes a transmitting transducer and a receiving transducer for generating a first responsive signal. The transmitting transducer and the receiving transducer are arranged on a chordal path. The second transducer is mounted on the conduit for generating a second responsive signal. The processor is configured to receive the first responsive signal and the second responsive signal, select one responsive signal according to a relationship of the first responsive signal and noise thereof and a relationship of the second responsive signal and noise thereof, and determine a flow rate of a flow medium according to the selected responsive signal. A method for measuring the flow rate of the fluid medium is also provided.