A calibration element (1) serves for calibrating the magnification ratio of a camera (3). The calibration element (1) has at least one calibration region (4) in which at least one perforation (5) or indentation is provided. The perforation (5) or indentation can be detected by the camera. The calibration element (1) is sufficiently slight in the calibration region (4) that the detection of an upper edge or lower edge of the perforation (5) or indentation produces only negligible differences. In order to determine the dependence of the magnification ratio on the thickness, the calibration element (1) additionally has at least one support foot (8), whose length (9) is selected in such a way as thereby to produce a variation in the measured magnification ratio of the camera image that can be evaluated.