This may well be a textbook question, or even a duplicate in this forum, but I have no idea of how to compute the capacitance between two conductors in the general case: all the computations I saw in textbooks make heavy use of symmetries to compute the capacitance, e.g. capacitance between two infinite planes separated by a fixed distance d, two concentric spheres etc. But in the general case, even if there is no solution in terms of elementary functions, how to attack this problem whenever symmetries are not available ? if only a simulation is possible, what is the exact method to obtain the simulation ? As a practical example, I would like to compute (or simulate) the exact capacitance between two rectangular planes at fixed distance d, separated by a dielectric ε (but without approximating the planes by infinite planes). Note: The following points are know and need not be explained here: * The potential inside and at the surfaces of the the conductors is constant * The field inside the conductors is null * The field at the surfaces of the conductors is normal to the surfaces * Gauss law EDIT: In the following link, the author says that it has searched for a formula unsuccessfully, and that he finally derived it himself (but does not explain how): http://chemandy.com/calculators/rectangular-capacitor-calculator.htm Please, see the comments of the author there.