Interactive LC Resonance Calculator
Calculate resonant frequency (f), inductance (L), or capacitance (C) using the resonance relationship.
What Is an LC Resonant Circuit?
An LC resonant circuit is a basic electrical network made from an inductor (L) and a capacitor (C). Together, they naturally oscillate at a specific frequency called the resonant frequency. At this frequency, energy continuously swaps between the magnetic field of the inductor and the electric field of the capacitor.
This behavior is central to radio receivers, filters, oscillators, impedance matching, and many RF systems. If you've ever tuned a radio station, resonance is part of what allows your circuit to "select" one signal from many.
Core Formula Used in This Calculator
The standard ideal resonance equation is:
- f = resonant frequency in hertz (Hz)
- L = inductance in henries (H)
- C = capacitance in farads (F)
Rearranging this formula lets you solve for L or C if the other values are known:
C = 1 / ((2πf)2L)
How to Use the Calculator
Step-by-step workflow
- Choose what you want to solve for: frequency, inductance, or capacitance.
- Enter the two known values.
- Select units for each known value (Hz/kHz/MHz/GHz, H/mH/µH/nH, F/mF/µF/nF/pF).
- Click Calculate to see the result and derived values.
The calculator also reports angular frequency ω0, period T, and the magnitude of reactance at resonance (|XL| = |XC|), which can be useful when checking practical designs.
Worked Examples
Example 1: Find resonant frequency
Suppose L = 10 µH and C = 100 pF. Plugging into the equation gives a resonance near the MHz range, commonly seen in RF front-end tuning circuits.
Example 2: Find required capacitor for a target frequency
If you need a resonant frequency of 455 kHz (classic IF frequency) and have a fixed inductor, this calculator can directly estimate the capacitor value needed for tuning.
Series vs. Parallel Resonance (Quick Context)
The same resonance math appears in both series and parallel LC networks, but circuit behavior differs:
- Series LC: impedance is minimum at resonance (acts like a short in ideal conditions).
- Parallel LC: impedance is maximum at resonance (acts like an open in ideal conditions).
In real designs, parasitic resistance and component non-idealities shift these ideal outcomes, but the ideal frequency estimate is still your design starting point.
Practical Design Notes
1) Component tolerances matter
A 5% inductor and 5% capacitor can produce noticeable resonant frequency variation. For stable systems, use tighter tolerance parts or provide tuning capability.
2) Parasitics become important at high frequency
Real inductors have winding capacitance and series resistance. Real capacitors have equivalent series resistance (ESR) and sometimes inductance (ESL). At higher frequencies, these parasitics can move resonance significantly.
3) Q factor controls sharpness
Resonance alone does not tell you bandwidth. The quality factor Q sets how narrow and selective the peak is. High-Q circuits are more selective but also more sensitive to variation and loading.
FAQ
Why does a tiny capacitance change the frequency so much?
Because frequency depends on the square root of LC. When L is small and C is in pF range, even small absolute changes are large relative changes, causing noticeable frequency movement.
Can I use this for audio-frequency LC circuits?
Yes. The equations are frequency-agnostic. Just be sure component values are practical for your range, and account for losses in real hardware.
Is this calculator for ideal or real circuits?
It is for ideal LC resonance. Use the result as a baseline, then refine with measured parasitics, simulator data, and lab tuning.
Final Thoughts
LC resonance is one of the most useful concepts in electronics. A quick calculator removes repetitive math, speeds early design, and helps verify hand calculations. Use this tool for first-pass design, then validate in simulation and measurement for production-quality results.