LC Resonance Calculator
Calculate the resonant frequency, inductance, capacitance, reactance, and wavelength of a series LC circuit, with optional series resistance for Q factor and bandwidth.
FreeOnline Tool
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How to Use
The defaults are 100 μH and 100 pF, which resonate at about 1.5915 MHz.
- Choose what to solve for: resonant frequency f₀, inductance L, or capacitance C. The matching input is disabled and derived from the other two values.
- Enter inductance and capacitance with units. Inductance supports H, mH, μH, and nH; capacitance supports F, mF, μF, nF, and pF; frequency supports Hz, kHz, MHz, and GHz.
- To get Q factor and -3 dB bandwidth, enter a series resistance R greater than zero. Leave it blank or set it to 0 to treat the circuit as ideal and hide those two results.
- The result cards show f₀, L, C, XL, XC, and wavelength λ. When R is provided, Q and BW appear as well.
- “Copy result” copies everything. “Load sample” restores 100 μH, 100 pF, and R = 10 Ω.
Features
- Three solve targets: find f₀ from L and C, find L from a target frequency and C, or find C from a target frequency and L.
- Series resonance formulas: f₀ = 1/(2π√(LC)) and at resonance XL = XC = 2πf₀L; capacitive reactance is also computed separately as 1/(2πf₀C).
- Optional Q and bandwidth: with a series resistance R, the tool computes Q = XL/R and BW = f₀/Q. Blank or zero R is treated as an ideal lossless circuit.
- Wavelength: λ = c/f₀ using the vacuum speed of light c = 299792458 m/s, displayed automatically in km, m, cm, or mm.
- Engineering units: common inductance, capacitance, and frequency units are converted internally, and results are scaled automatically.
- Validation: L, C, and f₀ must be greater than zero; R cannot be negative; out-of-range combinations return a clear error.
Use Cases
RF front-end tank design
Given a target center frequency and available capacitor values, solve for the inductance and check whether the reactances at resonance are reasonable.
Verify LC filter values
Enter the nominal inductance and capacitance you already have to see the actual resonant frequency and whether it lands in the intended band.
Estimate Q and bandwidth
Add the known series equivalent resistance to get Q and -3 dB bandwidth for an initial trade-off between selectivity and loss.
Antenna and line length sizing
Check the vacuum wavelength at the resonant frequency as a first-order reference for antenna dimensions or transmission-line lengths.
FAQ
Why do Q and bandwidth only appear after entering R?
Q = XL/R, so a series resistance is required to define loss. With R blank or zero the circuit is treated as ideal lossless, Q approaches infinity and bandwidth approaches zero, so the tool hides those cards and shows a note instead.
Does this tool support parallel LC resonance?
No. It models a series LC loop with f₀ = 1/(2π√(LC)). A parallel tank has a different equivalent impedance and Q definition, so Q = XL/R here does not apply to it.
How is the wavelength calculated and what is it for?
It uses λ = c/f₀ with the vacuum speed of light, 299792458 m/s. This is a reference for antenna, transmission-line, or filter dimension estimates; in a real dielectric the wavelength is shorter.
Which units are supported, and is scientific notation allowed?
Inductance: H, mH, μH, nH. Capacitance: F, mF, μF, nF, pF. Frequency: Hz, kHz, MHz, GHz. Both decimal and scientific notation are accepted. Values are converted to H, F, and Hz internally.
Why can measured results differ from the calculation?
The model is an ideal series resonant circuit. It ignores inductor and capacitor ESR, stray capacitance, core loss, load effects, and temperature drift. Use measurements for final tuning and allow for component tolerances.