The effect of adhesion on nanoscale indentation experiments makes the interpretation offorce–displacement curves acquired in these experiments very difficult. The indentationforce results from the addition of adhesive and elastic forces at the indenter–samplecontact. The evolution of the two forces during the indentation is determined by thevariation of the indenter–sample contact radius. In the present work the variation ofcontact radius during atomic force microscopy (AFM) indentation of elastic andadhesive samples with conical indenters (AFM tips) is indirectly determined bymeasurements of the contact dynamic stiffness. For weak sample deformations, thecontact radius is determined mainly by the adhesion force and indenter apex radius.For strong sample deformations, the contact radius increases linearly with theincrease of the indenter displacement, the slope of this linear dependence beingin agreement with Sneddon’s theory of indentation (Sneddon 1965 Int. J. Eng.Sci. 3 47). Based on these results, a theoretical expression of indentation forcedependence on displacement is found. This expression allows for determination of thethermodynamic work of adhesion at the indenter–sample interface and the sample elasticitymodulus.