Inductance of a Single Layer Close Wound Coil
Written by Bryce Ringwood   

This program provides a means of determining the number of turns required, or the diameter or the inductance of a single layer (close wound if wire diameter = pitch) coil. Accurate to about 1% for normal not thin not fat coils.


Used to calculate coils for radio circuits in the HF range.


Coil Parameters
Coil Parameters


Data Entry Section

Enter the unknown quantity as zero. Press "Calculate" Button to get the third quantity. 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.!


Enter /Calculate Number of turns N        

Enter / Calculate Former Diameter M     

Enter/Calculate Winding Pitch M         

Enter/Calculate Inductance  Henry's      


Additional Results


Winding length - Metres               

Wire length - Metres                   



Example - 40m Shortwave Coil

A coil has to be rewound for the 40m band of a short wave radio. The required inductance is 2.5µH. The coil former has an outside diameter of 10mm. How many turns are needed at a pitch of 0.5mm? - See the sample data.


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}= {{N^2}{R^2}\over {9R + 10Len}}}

The above formula for Inductance in µH is in imperal units, so we have to divide the right side of the equation by 25.4 to work in mm. $Len$ is length of winding = No of turns $N$ multiplied by pitch.


HP HP65 EEPac - Electrical Programs for HP65 Calculator.

See Also "Radiotron Designers Hanbook" - The "Red Book".

Correction to Pitch 16 Dec 2013

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