Resonant Frequency Calculator


Calculate the resonant frequency, inductance, or capacitance of a coil from any two values with the Resonant Frequency Calculator and learn on the go 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 the value that you would like to calculate

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

Selecting units: You can choose your preferred units of measurement through selecting the units cells and clicking the downwards pointing arrow to display a list of available options

Learn As You Go: This feature displays a live example of how to perform the calculation using the figures that you enter

Reference: ARRL – The Radio Amateur’s Handbook