LC Resonant Frequency Calculator

What is the LC Resonant Frequency Calculator?

This calculator finds the nominal resonance associated with one ideal inductor L and capacitor C. It can also solve either component for a target resonant frequency. The result includes a nominal period and verifies that inductive and capacitive reactance magnitudes agree at the calculated frequency.

This is a joint LC relationship. The existing Reactance Calculator instead evaluates one ideal component at a chosen frequency. Ideal series and parallel LC arrangements share the same reference frequency, but their input impedances and real loading behavior differ. This tool does not treat them as interchangeable complete circuit designs.

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Optional lcr meters (paid link) can check components at the instrument’s measurement frequency. No purchase is required, and a nominal measurement is not a complete RF or power-circuit characterization.

How to calculate LC resonant frequency, inductance or capacitance

1. Choose resonant frequency, inductance or capacitance as the unknown.
2. Enter the two visible known quantities with their units.
3. Use positive values; zero or negative L, C and target frequency are outside this model.
4. Calculate, then review the result, units and reactance-equality check.

Inductance units are nH, µH, mH and H; capacitance units are pF, nF, µF, mF and F. Frequency supports Hz, kHz, MHz and GHz. Unit changes convert a valid entered number to preserve its represented quantity and clear the previous result. Hidden unknown fields are disabled and ignored.

Optional inductor assortments (paid link) need datasheet checks for inductance at operating current, winding resistance, saturation and self-resonance. The tool does not infer these characteristics from an inductance entry.

LC resonance formula and inverse component equations

Use henries, farads and hertz. Angular frequency is in radians per second and differs from ordinary frequency by a factor of 2π. A common mistake is entering µH or pF numbers directly into a base-unit formula without converting them first.

The equality follows by setting the ideal reactance magnitudes equal. Capacitive and inductive signed reactances have opposite signs. Equality identifies this ideal LC reference frequency; it does not establish a real circuit’s Q, bandwidth, maximum voltage or permissible current.

LC resonant frequency calculation examples

For L = 10 mH = 0.01 H and C = 100 nF = 0.0000001 F, LC = 1e−9 H·F. Thus f0 = 1/(2π√(1e−9)) ≈ 5.032921 kHz. One nominal period is about 198.6918 µs. At this frequency, XL and |XC| are both about 316.2278 Ω.

To target 1 MHz using C = 100 pF, choose inductance as the unknown. L = 1/[(2π × 1,000,000)² × 1e−10] ≈ 0.0002533030 H = 253.3030 µH. The inverse calculation adds a step that substitutes the solved value back into the resonance formula.

With fixed L, multiplying C by four halves the ideal resonant frequency. Small component changes shift it continuously; choosing a nearby preferred part changes the nominal answer. For a reducible capacitor group, the Series & Parallel Capacitor Calculator can provide an ideal equivalent before applying a valid single-LC model.

Understand LC tank resonance and component self-resonance

An ideal series LC pair has cancelling net reactance at f0. An ideal parallel pair has cancelling net susceptance at the same reference frequency. Their ideal input impedances behave differently, and real losses and source/load coupling limit and can shift the observed response. The calculator deliberately reports a nominal frequency, not an infinite physical current or voltage.

Component self-resonant frequency is a separate property arising from an inductor’s parasitic capacitance or a capacitor’s parasitic inductance. Entering nominal L and C does not tell the tool either component’s parasitics. An LC tank estimate should not be mistaken for a manufacturer-specified self-resonant frequency.

Optional capacitor assortments (paid link) should be checked for dielectric, tolerance, ESR, voltage rating and frequency behavior. For an unloaded resistor-capacitor cutoff rather than LC resonance, use the RC Low-Pass & High-Pass Filter Calculator.

Accuracy and limitations of ideal LC resonance

Entered L must represent 1e−12–1e6 H; C 1e−15–1,000 F; and target frequency 1e−9–1e12 Hz. Calculated frequency or inverse components can fall outside entry bounds. These ranges are numerical limits, not evidence that a physical component will operate ideally at the resulting frequency.

The model excludes losses, winding resistance, ESR, parasitics, magnetic saturation, component tolerance, temperature effects, external coupling and source/load impedance. It does not compute Q factor, bandwidth, damping, loaded resonant frequency, oscillator startup or amplitude. A real parallel RLC circuit with particular loss placement may need a different resonance condition.

Results show seven significant digits with floating-point arithmetic. Optional digital oscilloscopes (paid link) must be appropriate to the actual circuit and probes. This is not an RF matching network, transmitter design, mains wiring or component-rating tool. For the standard RC timing of a separate oscillator IC, use the 555 Timer Calculator.

LC Resonant Frequency Calculator FAQs

Sources and methodology

Independently implemented standard ideal-circuit equations, reviewed October 27, 2026. Linked organizations do not endorse this tool. The exact manufacturer datasheet governs real component limits.

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