A method and apparatus for non-destructively measuring the internal volume and nominal diameter of cylindrical or substantially cylindrical bores. The apparatus includes an expander with an expandable outer skin, the expander is configured to be inserted into the bore being measured. A fluid contained within a pump associated with the expander is forced into the expander. The fluid causes the skin to expand and press against the side of the bore being measured. The quantity of fluid required to press the expander skin against the bore is related to the internal volume and nominal diameter of the bore.