# 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

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