If they're air core, it's pretty easy: To an accuracy of about 1%, the inductance in microhenries of an air-core coil is given by the formula:
L = a**2 n**2 ----------- 9*a + 10*b
where
a is the radius of the coil in inches b is the length of the coil in inches n is the number of turns.
Note that it's easy to get the turns count too low by 1/2 or 1 turn: a hairpin counts as 1 turn. Also this formula works best for coils with many turns.
Cheers,
Phil Hobbs