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Multilayer air coils

Multilayer air core inductor design calculator

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.

$$L(\mu H)=\frac{31.6*N^2*r1^2}{(6*r1+9*L+10*(r2-r1))}$$

  • 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
Multilayer air cor inductors

NOTEThis formula applies at ‘low’ frequencies (<3MHz) using
enameled copper wire tightly wound.

Multilayer air coils 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):
Coil Inner Diameter (d=2*r1):
Coil Length (l):
Wire Gauge: AWG
Number of Turns (N): turns
Turns per Layer: turns/layer
Number of Layers: layers
Coil Outer Diameter (D):
Wire Diameter:
Wire Length:
DC Resistance (R): Ω (at 20°C)

Multilayer air core inductors are often used in audio filter circuits and loudspeakers.

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