Abstract: An optoelectronic apparatus is set forth for measuring structural sizes or object sizes which has a light reception element for converting received light into image data, a reception optics arranged before the light reception element as well as an evaluation unit which is configured to identify structures or objects in the image data, to determine its dimensions in picture elements and to convert the dimensions into absolute, in particular metric, units of length with reference to a scaling factor, wherein the scaling factor can be determined in a calibration procedure. In this respect, the evaluation unit is configured to locate code regions in the image data and to read out code information from the code regions and to calculate the scaling factor during the calibration procedure from dimensions of a calibration code whose code information includes a size indication for the calibration code in the absolute units of length.