Abstract: A locking orthodontic band gauge for determining an orthodontic band size. An elongated main portion is provided with a locking indicator assembly slidably mounted thereon. A loop cooperates with the main portion and indicator assembly such that when the indicator assembly is slid along the main portion, the size of the loop circumference changes. A series of locking portions are provided and spaced along the length of the elongated main portion at discrete positions and cooperate with the locking indicator assembly to selectively lock the indicator assembly at the discrete positions. Alternatively the orthodontic band gauge includes a probe for supporting a gauge tape such that the gauge tape can be fitted around the tooth when the probe is inserted into a patient's mouth. The probe has an indicator associated therewith and moveable relative to the probe for indicating the orthodontic band size of a patient's tooth when the gauge tape is fitted around the tooth.