Calculation of Inductance of an Air Cored coil

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

d (coil diameter in inches) (mm)
len (coil length in inches) (mm)
 n (number of turns)
L (Inductance)   (uH)     (wire length inches)
maximum wire diam (in) (mm)
hover for   millimeters to AWG and SWG to millimetres   assistance
note: AWG sizes tend to be 1 or 2 sizes smaller than SWG sizes. e.g. 14awg = 16swg
millimeter to AWG conversion:
Enter Wire diameter in mm  excluding insulation (0.01 - 8.0mm)
Equivalent wire gauge:   AWG  Ø inches
Cross sectional area:  mm2  inches2
SWG to millimetre conversion:
Enter Wire gauge  use Whole Numbers 1 to 50 only.
Nearest Wire size  Ø mm  Ø inches
Cross sectional area:  mm2  inches2