On Sun, 17 Jun 2007 09:25:43 -0700, John Smith I
wrote:

Anyone have a reasonably accurate equation for such?

This does not work for structures with any significant size in
relation to wavelength.

A simple example reveals this with your inductance formula for a 1mm
thick 10 meter whip in the 20M band which suggests it "should be" 50.8
(whatever units your formula reveals). Experience informs us it is
not. This formula similarly fails throughout HF (and in fact would
lead us to the conclusion it was capacitive, not inductive at all).

Such formulas are generally useful at 1Khz (or where otherwise
specified).

73's
Richard Clark, KB7QHC