In this work, the electrostatic behaviour of nanometer-sized metallic floating conductors embedded in a dielectric medium has been investigated. First of all, we present a semi-analytical approach based on Green functions and show its excellent quantitative agreement with well known finite element methods concerning electrostatic computations. Then, we compare floating potential values obtained by numerical simulation with an approach based on an equivalent capacitor circuit. We show that the latter is inappropriate for sub-100 nm wide floating electrodes when the parallel plates approximation (PPA) is used to estimate the coupling capacitance values because of lateral coupling effects. Nevertheless, we finally show that these coupling capacitances can be easily extracted to predict the electrostatic potential of metallic nano-dots with the same accuracy than with a direct numerical computation. We finally propose a figure of merit to estimate the validity of the PPA. These results are useful to predict the floating potential of future generations of non-volatile-memories using metallic dots. Moreover they can be used to give a first estimation of the floating potential in a self consistent Poisson-Schrodinger resolution when considering semiconductor nanocrystals. (C) 2007 Elsevier Ltd. All rights reserved.