Inductance of a Layer Wound Coil
Written by Bryce Ringwood   

This program provides a means of determining the number of turns required, for a given inductance of a multi layer  coil. Accurate to about 1% for normal not thin not fat coils.


Used to calculate coils for radio circuits in the LF-MF range.

Illustration for Wheeler Formula
Coil Parameters


Data Entry Section

Enter L or N as zero. Press "Calculate" Button to get the result. In this program, SI suffixes can be used on input, and are used on output. For example, you can enter 1k for 1000 Ohms - and so on. !Be a bit careful here 10m = 10 millimetres; 500u=0.5m=0.5 millimetres; 2.5u=2.5 microHenries.!  Note that  you might have to mess about to find the outside diameter. Remember that a ferrite core can double the inductance.

Enter / Outside Diameter Db Metres             

Enter / Calculate Former Diameter Da Metres   

Enter Winding Len - Len Metres                

Inductance in Henrys  (if Known) or 0         

 Number of turns required (if Known or 0)     


Additional Results


Wire length - Metres  roughly           



Example - 450kHz I.F Coil for a Valve Communication Receiver

A coil has to be rewound for a 450kHz IF transformer for a short wave radio. The required inductance is 62.5µH. The coil former has an outside diameter of 7.6mm. How many turns are needed at a winding length of 12.5mm and an estimated outside diameter of 11mm ? - See the sample data. The inductance required has been divided by 1.5 because the coil has a ferrite core.


There is no theoretical basis for the following formula, as far as I know.

The formula was named after a Harold A Wheeler who worked it out empirically.


\displaystyle{{L} ={ {(31.6*{N^2}*{Ra^2})}\over {6*Ra + 9*Len + 10*(Rb - Ra))}}}

The above formula for Inductance in µH is in metric units. $Len$ is length of winding pile.




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