Ultrasonic Velocity Profile (UVP) method can be applied and succeeded for complicated flow as short inlet length from the double bent pipe. However, the flow of out-of-plane double bent pipe is more complicated and also more difficult to measure the highly accurate flowrate compare to in-plane double bent pipe. To solve this difficultly, the precise three-dimensional velocity profile forming is necessary. Multiple measurement lines are investigated for the out of plane double bent pipe to form the three-dimensional velocity profile. Moreover, the multiple measurement lines ultrasonic flow metering needs to optimize the number of measurement lines. In addition, the distance from the outlet to the measurement point as inlet length is also important. Therefore, the aims of this study are both estimate the optimal number of measurement lines and find out the minimum inlet length to measure the accurate flowrate on the out-of-plane double bent pipe by using a sampling transducers rating estimation method with signal processing technique. The minimization of the inlet length was started from 3 D, 4 D and 5 D. The estimation of optimal number of measurement lines was executed in the condition of Re~40,000. The out-of-plane double bent pipe was spread the out-of- plane angle at 0°, 8° and 16°. In this study, the circumferential velocity profiles are reconstructed from many velocity profiles measured around the center of pipe using single measurement lines. These circumferential velocity profiles come as the form of wave. Fourier Transform technique (FT) changes the waveform data to design the number of measurement lines by using sampling rate theory.