A measuring device determines a distance between a processing head for a laser processing system configured to process a workpiece with a laser beam and the workpiece. The measuring device includes an optical coherence tomograph to measure a distance between the processing head and workpiece. In the optical coherence tomograph, measuring light generated by a measuring light source and reflected by the workpiece interferes with measuring light reflected in a reference arm with two or more reference stages. The stages include a first reference stage configured such that the measuring light reflected therein travels a first optical path length, and a second reference stage configured such that the measuring light reflected therein travels a second optical path length different from the first length, wherein the measuring light reflected by the workpiece interferes with reflected measuring light of the first reference stage and reflected measuring light of the second reference stage.