Clamp-on ultrasonic flow metering can provide a non-invasive and portable means for flow measurement. However, the clamp-on ultrasonic flow metering indicates flow rates with low measurement accuracy at low flow velocity in pipe flows. Typical accuracy of the clamp-on ultrasonic flow metering amounts as low as ±1 % if the flow velocity in a pipe is greater than 0.5 m/s. The accuracy can be greater than ±2 % if the flow velocity is lowered smaller than 0.5 m/s. These shortcomings of the clamp-on ultrasonic flow metering can be overcome by combining two transit times along a Z-shaped and a V-shaped ultrasonic path. This technique is named as combined V/Z clamp-on ultrasonic flow metering. With the water flow standard system in KRISS, this combined technique exhibited intermediate performance between the two flow metering techniques along the Z-shaped and the V-shaped ultrasonic paths.