I've been looking for a good formula to calculate the inductance of a multilayer solenoid within about 10% accuracy or greater. I've used several formulas derived from Wheeler's formula, as well as a few online calculators, however, my results seem to differ wildly depending on what formula or calculator I use. I'm wondering if anyone has a formula or calculator for multilayer coils consisting of only a few layers that they've found works well. If it helps the wire is .225 millimeters in diameter, the coils are less than 2 cm long with maybe 2 or three layers, and the diameter of the tubing is 5 millimeters. Thanks!