Abstract: A liquid storage tank contents gauge comprises means providing an electrical signal corresponding to the vertical height of the liquid in a tank in the form of an ultrasonic transducer positioned at the base of the tank and emitting a pulse of acoustic energy vertically upwards and which detects the pulse when reflected from the liquid/air interface within the tank and including timing means provided to time the interval between the emission of the pulse and the detection of the reflected pulse, electronic means for deriving the volume of liquid corresponding to the vertical height, and an output means for providing a visual output of this volume.