This paper describes a method to accurately determine the distance between a transmitter and receiver in an Ultrasonic Ranging System. The method has an accuracy associated with phase measurement systems, which are more accurate than typical ranging systems that use magnitude thresholding to measure time-of-flight (TOF). The significance of the method described is that the maximum measurement range is not limited to one wavelength (or one period) of the acoustic wave used. This limitation is typical of phase-based ranging systems. The maximum range is limited only by the method used to measure TOF, which in our case was the maximum count of a 16-bit counter at 1 MHz clock rate. The acoustic ranging system described uses simple circuitry to extract a digital pulse with a duration equivalent to the TOF. The prototype system developed is very stable and robust, and it exhibits an accuracy of ±0.295 mm at a range of 0.5842 m. This accuracy could be further improved by compensating for variations in the speed of sound caused by temperature variations.