A confocal microscope for determination of a layer thickness comprises: a focus adjusting device configured to adjust a relative displacement between a focus position of the illumination light and a specimen position along an optical axis, wherein measurement signals belonging to different settings of the focus adjusting device can be recorded; an evaluation device for determining a specimen layer thickness as follows: determine intensity band positions of two intensity bands in a measurement graph recorded by a light measuring device, the measurement graph indicating a light intensity in dependence of the focus position; determine a layer thickness on the basis of a positional difference between the intensity band positions; and determine the layer thickness using a mathematical model which describes for overlapping intensity bands a dependence of the intensity band positions on a light wavelength and the layer thickness, considering interference of the illumination light at the layer.