Abstract Numerous materials are affected by the Indentation-Size-Effect (ISE). Thus, the interpretation of ISE-influenced indentation data plays an important role. This paper presents a method which allows for the characterization of the ISE using the loading curvature C of a single load-displacement curve (P–h curve) from sharp indentation. The method is based on the analysis of the change of the parameter C as a function of the indentation depth as described by Kick ’s law (related to the universal hardness or also called Martens hardness HM). The intensity as well as the indentation depth where the ISE is saturated can be detected. Furthermore, it allows for the correction of ISE-affected loading curves with the use of the Vickers macro hardness. For example, this can enable the application of inverse methods for ISE-affected materials or phases. Mechanically polished samples show an additional increase in strength during nanoindentation due to hardened surface layers. The presented method also accounts for this influence and can correct affected loading curves. It was applied to the austenitic stainless steel X2CrNi18-9 (AISI 304L) which is heavily affected and the C45 carbon steel which is slightly affected by the ISE. The influence of hardened surface layers was investigated using electropolished and mechanically polished AISI 304L.