LC Constant Calculator

Calculate the inductance or capacitance of a resonant circuit with the LC Constant 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 (L) and capacitance (C) is constant. The relation between the two for a fixed frequency is called the L/C ratio.

When the frequency is known, and either the inductance or the capacitance is known, you can calculate the unknown quantity using the LC Constant Calculator. The inductance or capacitance required for resonance at any frequency is given by the equation:

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

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

Example 1: Find the capacitance required to resonate at 1860 kc (1.86 Mc) with an inductance of 250 µH

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

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

Example 2: Find the inductance required to resonate at 570 kc (0.57 Mc) with a capacitance of 1500 pF

$LC=\frac{25,330}{0.57^2}=\frac{25,330}{0.3249}=77962.5$

$L=\frac{77962.5}{C}=\frac{77962.5}{1500}=51.975\; \mu H$

Using the LC Constant Calculator

Frequency: You must enter a frequency for the calculator to work

Calculating inductance: To calculate the inductance, input the capacitance into the green capacitance cell

Calculating capacitance: To calculate the capacitance, input the inductance into the green inductance cell

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