Calculating Capacitance

Either apply Maxwell's equations and the materials-specific response equations and do a 3-d solution of the electric field everywhere, squaring and integrating over all space to determine stored energy, or find someone who knows a dozen crufty approximations and can get it good enough. Or, build something that looks kinda right, and determine the capacitance by measurement.

I like the guesstimate, then measurement approach.

George H.