The formula used in this
calculation is from the famous Harold A. Wheelers approximations
which is accurate to <1% if the cross section is near
square shaped.
$$L(\mu H)=\frac{31.6*N^2*r1^2}{(6*r1+9*L+10*(r2r1))}$$
where…
 L(uH)= Inductance in microHenries
 N = Total Number of turns
 r1 = Radius of the inside of the coil in meters
 r2 = Radius of the outside of the coil in meters
 L = Length of the coil in meters


NOTEThis formula applies at ‘low’ frequencies (<3MHz) using
enameled copper wire tightly wound.
Please note that the diameter is measured from center of wire trough
center of the coil and to center of the wire on the opposite side.