The following formula calculates the inductance of an air cored single layer coil.
L= ( d2 x n2)
(18 x d + 40 x len )
where:- L is the inductance in micro Henrys, d is the coil diameter (cntr-cntr) in inches (form diameter plus the wire), len is the coil winding length in inches
and n is the number of turns.
"Wire length" allows for approximately a 2 inch tail at each end