Abstract: Systems and methods for providing an ultrasonic depth gauge. The depth gauge accurately measures the depth of a drill hole in a bone using ultrasonic waves so that an appropriately-sized bone screw may be selected. The ultrasonic depth gauge includes a probe that is selectively insertable and extendable into a drill hole of a bone. The probe includes an ultrasonic transducer positioned at a distal end that is operative to detect when the probe has extended through the entire drill hole by detecting changes in echo signals. The gauge also includes a sensor for measuring the length of the probe inside of the drill hole when the probe is extending through the entire depth of the drill hole. Using this measured length, the depth of the drill hole may be accurately determined.