Published July 10, 2014. Updated February 13, 2021.

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

The wire length is calculated as an average of the evenly spaced turns, this results in a estimated spiral length from being calculated as single circles.

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