As ultrasonic pulsed Doppler has many advantages, it has been widely used for measuring velocity profiles. By integrating the obtained velocity profile all over the pipe, flow rate can be derived. The authors have developed feedback method which is a dealiasing method for high flow rate measurement and reported that measurement accuracy was improved by applying a multi-wave ultrasonic transducer. In this paper, effect of the size of measurement volume was investigated analytically and experimentally. In the analysis, measured velocities were considered to be ensemble average over the measurement volume. Analytical results showed the effect of channel-width was more significant than that of the sensor diameter. Furthermore, results of experiments were in good agreement with the analysis.