Capacitance of a coil

OK coilers,

please help me on this: I'm writing a Tesla coil calc program (well,
just for me to understand it better and get familiair with the calcs),
but I don't know how to calculate the capacitance of a coil. I could of
course use Medhurst's formula (is there a table for H/D ratio > 5?), but
I wanted to know if there's another way to calc it too.

Thanks, Reinier

BTW: It's only going to handle metric units!