Formula:
\[
L = \frac{\mu_0 \mu_r}{2\pi} \cosh^{-1}\left(\frac{2H}{D}\right) \times L
\]
where:
\( \mu_0 = 4\pi \times 10^{-7} \, H/m \) (permeability of free space)
\( \mu_r \) = Relative Permeability
\( H \) = Height above plane
\( D \) = Diameter of wire
\( L \) = Length of wire