This paper presents a method for locating and measuring the size of cracks in beams by time of flight (ToF) of ultrasonic wave. The echo detected was processed using the stationary wavelet transform and the Hilbert transform. The accuracy of the information obtained from the processed signal depends on the selected mother wavelet. To select the best mother wavelet for signal processing were used the Shannon's entropy criterion. The ToFs were obtained from denoising process using the stationary wavelet transform and the envelope of the Hilbert transform. The uncertainties of the ToFs using Fuzzy numbers are also estimated in order to assessment the qualities of the ToF Measurement.