LCF Calculator
Pick exactly two knowns. Enter values. Click Calculate.
Select knowns (2)
Enter values
Frequency (f)
Capacitance (C)
Inductance (L)
Reactance (X)
Results
Frequency
–
Capacitance
–
Inductance
–
Reactance
–
Uses resonance: X = 2πfL = 1/(2πfC) and f = 1/(2π√(LC)).

The “LCF Calculator” solves an LC resonant relationship where any two of these values determine the other two: Frequency (f), Capacitance (C), Inductance (L), Reactance (X).

What this calculator helps you do

It helps you design and understand tuned circuits. Those show up any time you deal with antennas, filters, tuners, traps, or matching networks. If you work HF or VHF, you will use this more than you think.

You give it any two values. It tells you the other two. That saves trial and error.

Common real-world uses

Building an antenna trap
You want a trap that blocks 20 meters at 14.2 MHz.

  • You already have a 100 pF capacitor in your parts bin
  • You enter Frequency = 14.2 MHz
  • You enter Capacitance = 100 pF

The calculator tells you the inductance needed. You wind that coil and you are very close on the first try.

Designing a band-pass or band-stop filter
You want to reduce interference from a nearby repeater.

  • You know the frequency you want to reject
  • You want the reactance around 50 ohms to match your system

You enter Frequency and Reactance. The calculator gives you the L and C values needed for that filter section.

Understanding why your tuner works
An antenna tuner is just inductors and capacitors.

  • You tune for minimum SWR
  • Internally, the tuner is creating a specific reactance at a specific frequency

By entering the frequency and reactance, you can see what size L and C the tuner is effectively using. This helps you understand why some tuners work better on certain bands.

Choosing parts you already own
You do not always start with a clean design.

  • You find a box of coils or capacitors
  • You want to know what frequency they will resonate at

You enter Inductance and Capacitance. The calculator tells you the resonant frequency. That lets you reuse parts instead of guessing.

Checking VHF and UHF circuits
At VHF and up, small values matter.

  • A few picofarads or nanohenries can shift resonance a lot
  • PCB traces and leads add inductance and capacitance

You can plug in very small values and see how sensitive the circuit is before you build it.

Why reactance matters to you

Reactance is the part of impedance that causes SWR problems.

  • Too much inductive reactance and your antenna looks long
  • Too much capacitive reactance and it looks short

This calculator shows how L, C, frequency, and reactance are tied together. That makes antenna and matching problems easier to visualize.

When you would not use it

  • It does not replace a full antenna modeling program
  • It does not predict radiation pattern or efficiency
  • It does not account for losses or component Q

It is a quick design and sanity-check tool, not a simulator.

Bottom line for a ham

If you build things, repair things, or want to understand what is happening inside your station, this calculator saves time.

It turns “why does this work” into numbers you can actually use.