Piezoelectric semiconductor transducers based on nanowires (NWs) made of ZnO, GaN among other materials have drawn a lot of attention for energy harvesting and sensing applications. Despite the existence of experimental reports on the piezoelectric coefficient of ZnO NWs using Piezoelectric Force Microscopy (PFM), there is a lack of theoretical results predicting such measurements. Here we propose an experimental and a simulation framework consisting in the analysis of the exponential decay of a generated piezoelectric voltage pulse to extract the capacitance of ZnO NW based nanocomposites and the related. The theoretical results show a dependency on the NW radius, thus achieving high values (14 pC/N) at radius smaller than 70 nm.