Here you can calculate the inductance for a given size of a spiral coil wound in one layer. It is optional to add the capacitance for f.ex. a primary tank capacitor or topload capacitance to find the resonant frequency of the LC circuit.

The formulas used to derive the inductance is simplified and correct to within 1%. Source “Harold A. Wheeler, “Simple Inductance Formulas for Radio Coils,” Proceedings of the I.R.E., October 1928, pp. 1398-1400.”

Switch between the input fields to automatically calculate the values.

Formulas used

**Outer diameter** = inner diameter + ( 2 * number of turns * ( wire diameter + wire spacing))

**Wire length** = ((Pi * number of turns * (outer diameter + inner diameter)) / 2) / 1000

Inductance

Width w = ((wire diameter / 25.4) + (wire spacing / 25.4)) * number of turns

Radius r = ((inner diameter / 25.4) + w) / 2

**Inductance** = (radius^2 * number of turns^2) / (8 * radius + 11 * width)

**Resonant frequency** = (1 / (2 * pi * sqrt((inductance / 1000000) * (capacitance / 1000000000)))) / 1000

Thank you thank you

hello

i have a inductor how can i mak it?

L: 1.5 / 3mm 0.5CU 2.5 mm

Hi rubashka

Could you please describe in more details what it is you need.

Kind regards

Mads

Hello, I found this page through a Google search. Very informative. I do have one question, how do you arrive at inductance from the equation: (radius^2 * number of turns^2) / (8 * radius + 11 * width) when there is no permeability units in the formula? I get the same answer you do, but the units are in meters, not henries.

Thank you for your time,

David

Hi David

The formula is a simple approximation as described first in the article.

Permeability is in it, but only for air cored copper coils, this is all a part of Harolds work, he made it simple so you only have to put in some physical dimensions to get a estimated inductance.

Kind regards

Mads

Hi there,

I have 5 turns

inner diameter is : 18 mm

wire diameter is :0.2 mm

turn spacing is : 10 mm

outer diameter is : 52 mm

wire length : 0.5 meters

The capacitance I use is : 1.36 micro farad .

I could not change the value of outer dimater here so please tell me what is the inductance value.

Thanks in advance.

Hi Iyad

The outer diamter is calculated from inner diameter + number of turns (distance), so you should not put that value in, it is calculated.

Judging from your numbers and the picture, something is not right.

Kind regards

Mads

Hi,

I would have thought that since the inductance goes up as the square of the turns, where as the resistance is linear that I could get a higher Q with copper thin strips, and decreasing the turn spacing, but I don’t get the high Q I’m looking for (not more than 40-50 @ 100khz). Do you have any insight into this problem.

Hi,

What formula should I use to calculate the capacitance?

The formula I am using C=0.29l+0.41r+1.94*(r³/l)^0.5

I am using magnet wire 0.4mm², with ID of coil 1″ and 44 turns. I get a calculated capacitance of 71pF

Regards

David

Hi David

I would use the results from JAVATC as I consider this the best and most though-rough calculator available. My own calculator here is only meant for quick estimates where you can get a result from as few factors as possible. Consider it a ideal world with no losses example 🙂

http://www.classictesla.com/java/javatc3d/javatc3d.html

Kind regards

Mads

How to find circumferential area

In geometry, the area enclosed by a circle of radius r is = π * r * r