Atomic force acoustic microscopy (AFAM) is a dynamical AFM-based technique very promising for nondestructive analysis of local elastic properties of materials. AFAM technique represents a powerful investigation tool in order to retrieve quantitative evaluations of the mechanical parameters, even at nanoscale. The quantitative determination of elastic properties by AFAM technique is strongly influenced by a number of experimental parameters that, at present, are not fully under control. One of such issues is that the quantitative evaluation require the knowledge of the tip geometry effectively contacting the surface during the measurements. We present and discuss an experimental approach able to determine, at first, tip geometry from contact stiffness measurements and, on the basis of the achieved information, to measure sample indentation modulus. The reliability and the accuracy of the technique has been successfully tested on samples (Si, GaAs, and InP) with very well known structural and morphological properties and with indentation modulus widely reported in literature. (c) 2005 American Institute of Physics.