LC Resonance Calculator
Calculate the resonant frequency of an LC circuit.
How it works
An LC circuit (tank circuit) consists of an inductor (L) and a capacitor (C). At a specific frequency called the resonant frequency (f), the inductive reactance (XL) and capacitive reactance (XC) are equal in magnitude and opposite in phase, cancelling each other out.
f = 1 / (2π√(LC))
At resonance, the circuit stores electrical energy oscillating between the capacitor (electric field) and inductor (magnetic field).
Worked example
If you have a 10 µH inductor and a 100 nF capacitor:
L = 0.000010 H
C = 0.000000100 F
f = 1 / (2π√(0.000010 × 0.000000100)) ≈ 159,155 Hz (159 kHz)
At this frequency, XL = 2π(159155)(0.000010) ≈ 10 Ω, and XC ≈ 10 Ω.
Frequently Asked Questions
Are XL and XC always equal?
Only at the exact resonant frequency. Below resonance, the circuit is capacitive (XC > XL). Above resonance, it is inductive (XL > XC).
Does an LC circuit have a time constant like an RC circuit?
No. An LC circuit does not dissipate energy in resistance and does not have an exponential time constant (unlike RC circuits where τ = R × C or RL circuits where τ = L / R). Instead, an ideal LC tank circuit oscillates continuously at its resonant frequency f = 1 / (2π√(LC)). If you need charging or discharge timing calculations, see our RC Time Constant Calculator.
Sources
- Resonance theory for RLC circuits.
Results are for engineering assistance. Verify important calculations and check official datasheets. See the Engineering Disclaimer.