Resonant Frequency Calculator

Calculate the resonant frequency, inductance, or capacitance of a coil from any two values with the Resonant Frequency Calculator, and learn how with the integrated live example

The resonant frequency calculator can calculate the resonant frequency of a coil from the inductance and capacitance, calculate the inductance from the frequency and capacitance, or calculate the capacitance from the frequency and inductance.

Looking for the Coil Resonant Frequency Calculator?

The formula for the resonant frequency of a circuit shows that the same frequency will always be obtained as long as the product of the inductance and capacitance is constant. The relation between the two for a fixed frequency is called the L/C ratio. The resonant frequency formula is:

$f=\frac{1}{2\pi\sqrt{LC}}$

Where
L = Inductance in Henrys (H)
C = Capacitance in Farads (F)
f = Frequency in cycles per second (C.P.S.) or Hertz (Hz)

These units may be inconvenient when dealing with radio frequencies. An alternative formula is:

$f=\frac{10^6}{2\pi\sqrt{LC}}$

Where
L = Inductance in microhenrys (µH)
C = Capacitance in picofarads (pF)
f = Frequency in kilocycles (kc) or kilohertz (kHz)

Example 1: Using the resonant frequency formula, find the resonant frequency of a circuit with an inductance of 3.2 µH and capacitance of 970pF

$f=\frac{10^6}{6.28\sqrt{3.2\times 970}}=\frac{10^6}{6.28\times 55.71}$

$=\frac{10^6}{350.05}=2856.667\; kc$

Example 2: Using the LC Constant formula, find the capacitance required to resonate at 1860 kc (1.86 Mc) with an inductance of 250 µH

$LC=\frac{25,330}{1.86^2}=\frac{25,330}{3.4596}=7321.7$

$C=\frac{7321.7}{L}=\frac{7321.7}{250}=29.29\; pF$

LC Constant

The Resonant Frequency Calculator also uses the LC Constant to calculate the inductance or capacitance when the frequency is known. The LC Constant formula is:

$LC=\frac{25,330}{f^2}$

Where
L = Inductance in microhenrys (µH)
C = Capacitance in picofarads (pF)
f = Frequency in megacycles (Mc) or megahertz (MHz)

Using the Resonant Frequency Calculator

Select whether to calculate the Frequency, Inductance, or Capacitance

Inductance: Input the inductance and select your preferred units

Capacitance: Input the capacitance and select your preferred units

Frequency: Input the frequency and select your preferred units

How To Calculate Resonant Frequency: This feature displays a live example of how to perform the calculation using the figures that you enter

The result is calculated and updated automatically as you enter different numbers or change between the input fields. If the calculated result hasn’t updated after you’ve finished entering your values, click or tap on the result.

Reference: ARRL – The Radio Amateur’s Handbook