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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. $$L(\mu H)=\frac{31.6*N^2*r1^2}{(6*r1+9*L+10*(r2-r1))}$$ where… 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. Inductance (L): uHmHH Coil …

Winding the wire in a single layer produces an inductor with minimal parasitic capacitance, and hence gives the highest possible self-resonant frequency (SRF). Striving to obtain a high SRF and low losses is the key to producing coils which have radio-frequency properties bearing some useful resemblance to pure inductance. The calculation is based on Harold A. Wheeler’s 1928 formula for …

This is an popular coil geometri used in todays wireless charger circuits. The formula used in this calculation is based on the Harold A. Wheeler approximations for air core flat spiral coil inductor. …where: 1 inch = 0,0254m=2,54cm = 25,4mm. This formula applies at ‘low’ frequencies (<30MHz) using enameled copper wire. Some people call it “magnet wire”. Click on image …

The first approximation is based on a modification of an expression developed by Wheeler; the second is derived from electromagnetic principles by approximating the sides of the spirals as current-sheets; and the third is a monomial expression derived from fitting to a large database of inductors (and the exact inductance values). All three expressions are accurate, with typical errors of …