Abstract: A knife for cutting cartons comprises a movable blade carrier, and blade, mounted in a stepped guide for positive blade location at any of a plurality of selected locations, within a handle having an extended area lip feeler adjacent a handle opening such that the blade may be presented through said opening in any of a plurality of lengths corresponding essentially to the thickness or thinness of a carton wall so that the knife cuts the carton and not its contents, consistent with safety for the operator, economy of manufacture and use and compactness.