# Multilayer air core inductor design calculator info The formula used in this calculation is from the famous Wheelers approximations which is accurate to <1% if the cross section is near square shaped. L (uH) =31.6*N^2* r1^2 / 6*r1+ 9*L + 10*(r2-r1) where… L(uH)= Inductance in microHenries N = Total Number of turns r1 = Radius of the inside of the coil in meters r2 = Radius of the outside of the coil in meters L = Length of the coil in meters NOTEThis formula applies at ‘low’ frequencies (<3MHz) using
enameled copper wire tightly wound. 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 Inner Diameter (d=2*r1): inchesmmcm Coil Length (l): inchesmmcm Wire Gauge: 123456789101112131415161718192021222324252627282930313233343536373839404142434445 AWG Number of Turns (N): turns Turns per Layer: turns/layer Number of Layers: layers Coil Outer Diameter (D): inchesmmcm Wire Diameter: milsmm Wire Length: feetmeters DC Resistance (R): Ω (at 20°C)

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