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Dimensioning of coils for a ring inductor without core.

Inductor ring coiled in the air

It calculates the coils and construction parameters necessary to realize an inductor with the needed inductance value.
It is adapt for closed coils in free air (without core) or with not magnetic (circular) core.
Dimensioning is done with successive approximations using Wheeler method until obtain valid results and inner acceptable tolerances.

Input dati

Required inductance value


Inductor characteristic.

Diameter of the enamelled wire for coil:

Ø f (mm)


Inner diameter of the coil:

Ø i (mm)

Pack form ratio (L / H):

L / H

Wait calculate.
Dimensional data.
Imposed inner diameter Ø i mm
External diameter Ø e mm
Pack width L mm
Pack height H mm
Constructive data.
Total required coils n.
Turns per layer n.
Layers n.
Minimal length of the wire (closed coils) m
Wire resistance (copper) ohm
Wire weight (copper) kg

The support for the coil can be removed after the realization if during it, at the end of every layer, is spread a layer of glue or resin for winding.

Wire section used must be tailored for the current (1-3 A mm˛), to valuate it according to the power see page Dimensioning of cables for passive speakers. To exceed with the wire section is not an error.

To verify the inductance value realized see Resonant frequency of L-C circuit, with a capacitor (e.g. 1 µF) in parallel. Varying the input value of the inductance until obtain the same resonant frequency measured using a signal generator and the oscilloscope.

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