By introducing an electrostatic problem analogous to the impedance function problem it is found possible to prove that, under simple and quite broad assumptions, the maximum possible gain‐band width products for two‐terminal coupling, four‐terminal low‐pass coupling and four‐terminal band‐pass coupling are, respectively, 1, 2.47, and 2.53 times g/πC. The first result was conjectured by Wheeler long ago, and it and the second have recently been proved by Bode. The last result covers a case more general than those considered by Bode.