# Resonant Frequency Calculator

## Calculate the resonant frequency, inductance, or capacitance of a coil from any two values with the Resonant Frequency Calculator

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.

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:

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:

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

**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 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:

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*

## Additional information

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