Helical coil calculator

Here you can calculate the inductance for a given size of helical 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.

Coil diameter mm
Number of turns Turns
Wire diameter mm
Turn spacing mm
Wire length meters
Coil height mm
Inductance uH
Optional extra f.ex. tank/topload capacitance size
Capacitance nF
Resonant frequency kHz

Formulas used

Wire length in meters = ((coil diameter * pi) * number of turns) / 1000

Coil length in mm = number of turns * (wire diameter + turn spacing)

Coil inductance in uH = (number of turns * (((coil diameter / 25.4) / 2)*((coil diameter / 25.4) / 2))) / ((9 * ((coil diameter / 25.4) / 2)) + (10 * (coil length / 25.4)))

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

3 thoughts on “Helical coil calculator”

  1. Pingback: How to build a Tesla Coil. Design, Theory and Compromises! - opentesla.org

  2. 𝐿= (𝑁^2∗𝑐𝑑^2)/(25.4 ∗(18∗𝑐𝑑+40∗𝑐𝑙)) 𝜇𝐻
    𝑓𝑜𝑟 𝐻𝑒𝑙𝑖𝑐𝑎𝑙 𝑐𝑜𝑖𝑙 𝑎𝑖𝑟 𝑐𝑜𝑟𝑒 𝑖𝑛𝑑𝑢𝑐𝑡𝑜𝑟𝑠
    N = No of turns
    cd = coil dia, mm
    cl = coil length2, mm
    This is the correct formula

  3. Hi Saju
    That is actually also the formula used by the script, the formula written underneath is wrong.

    Single layer air core solenoid
    L (uH) = r^2 * n^2 / (9 * r + 10 * l)


    r = coil radius in inches
    l = coil length in inches
    n = number of turns

    So results from calculator are correct. Thanks for pointing out the error in the explanation 🙂
    Kind regards

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