In scanning probe techniques, accurate height measurements on heterogeneous surfaces are a major requirement. Different electrostatic potentials of various materials have a significant influence on the measured force/current and therefore a direct influence on the tip-sample distance. Kelvin probe force microscopy (KPFM) is based on a dynamic compensation of the electrostatic force while performing non-contact atomic force microscopy measurements. Thus, the influence of the electrostatic potentials can be minimized and accurate height measurements become possible. Here, the study of ultra-thin alkali halide films on Cu(111) investigated by KPFM is presented. This work is focused on the interface between areas of bare Cu(111) and the first layers of salt. The compensation of the electrostatic potential allow us to determine layer heights with high accuracy. The second objective was to elaborate on the characterization of tip geometries across suitable nanostructures. Simulations of measured images are performed with different input parameters, which gives a direct estimation of the effective tip radius and geometry used for the measurements.