A hand-held device for measuring the curvature of cylindrical or toroidal surfaces such as optical lenses. A longitudinally movable plunger or spindle extends from a rotationally adjustable indicator dial with its work-contact end bisecting a transverse support frame which carries a parallel pair of work-contact buttons spaced apart by the length of a chord of the curved work surface whose midspan is to be contacted by the plunger. The consequent dial read-out is a factor (in mm.) from which the curvature of the arc can be obtained, as by reference to tabulated data. The support frame is detachable from the indicator unit and a progressive series of such frames having buttons spaced apart by different chord lengths are provided for measuring both convex and concave workpieces of different curvatures. The pair of work-contact buttons are flat-ended cylinders which make point contact of an edge of the cylinder with an arcuate workpiece; when worn, such contact points can be shifted by rotating the button in the frame and thus maintain extreme precision of the instrument.