A method of ultrasound flow metering includes applying a first and second pulse train to an ultrasound transducer pair (T1, T2) positioned for coupling ultrasonic waves therebetween. Responsive to the first pulse train applied to T1, T1 transmits an ultrasonic wave received as received ultrasonic wave (R12) by T2 after propagating through fluid in a pipe. Responsive to the second pulse train applied to T2, T2 transmits an ultrasonic wave received as received ultrasonic wave by (R21) T1 after propagating through the fluid. During the pulse trains, R12 and R21 build up in amplitude to provide excitation portions. The pulse trains are terminated, so that R12 and R21 decay as a damped free oscillation. Windowing is applied to R12 and R21 to generate windowed portions. A signal delay between t12 and t21 (ΔTOF) is calculated using only windowed portions, and a fluid flow is calculated from the ΔTOF.