A method for measuring multi-level fluid, based on ultrasonic echo detection by means of the wavelet transform (WT), is presented. The Wavelet Transform provides a tool for analyzing the time frequency evolution of transient signals. This highlights the excellent performance shown by the WT as a powerful tool for the analysis of echoes in a noisy environment. A mother wavelet is utilized to obtain the time evolution of the various spectral components of the ultrasonic signal, and the decomposition of the wavelet transform is used to represent the envelope of the ultrasonic pulse and to determine the time of arrival of ultrasonic signal called Time-of-Flight (ToF). To this purpose, tests on simulated signals transmitting and receiving from multi-level fluid are carried out. The influence of uncertainties associated with additive noise and attenuation of the ultrasonic signal on the multi-level measurement uncertainty is analyzed. An application example is shown in order to illustrate the proposed procedure. © 2011 IEEE.