Electrostatic force microscopy (EFM) allows measurement of tiny changes in tip-sample capacitance. When nanoobjects are studied by EFM, they only contribute a very small fraction of the total capacitance between the tip and the sample. We show that the analysis of 3D maps of the EFM signal allows extracting the contribution of the nanomaterial to the total capacitance. This opens the way to applications of EFM as a measure of the dielectric coefficient of electrically insulating nanomaterials or the quantum capacitance of conducting nanomaterials. We apply this method to study the charge response of magnetite, Fe3O4, nanoparticles. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4790587]