Abstract: The diameter of a generally cylindrical roll is accurately measured by holding a gauge against the surface of an arc of the roll, determining the approximate variation in diameter from a standard diameter with a primary sensor located between two supports and determining corrections to the approximate variation in diameter through secondary sensors located adjacent to the supports. The gauge supports also indicate misalignment of the central plane of the gauge with a circumferential plane of the roll by lack of contact of the supports with the roll surface and by measurements of the secondary sensors over a predetermined amount.