RLC Resonance Calculator

A series RLC circuit — resistor, inductor, and capacitor all in one loop — has a resonant frequency where the inductor's reactance and the capacitor's reactance cancel each other out exactly, leaving the circuit purely resistive. This calculator finds that frequency as f₀ = 1/(2π√(LC)), derived from setting the inductive and capacitive reactances equal, and reports the impedance at that point as simply R, since the reactive components cancel to zero. The Q factor, Q = (1/R)√(L/C), measures how sharply peaked the resonance is: a low-resistance circuit with a large inductance-to-capacitance ratio "rings" strongly and selects a narrow range of frequencies, while high resistance damps the response into a broad, shallow peak. Bandwidth (BW = f₀/Q) is the width of that resonance peak between the two "-3dB" points — the lower and upper frequencies where the circuit's response has dropped to about 70.7% of its peak value, computed here from a standard approximation involving Q and f₀.

The impedance-vs-frequency chart sweeps a logarithmic frequency range centered on resonance so you can see the characteristic V-shaped impedance dip (impedance is high away from resonance, where reactance dominates, and dips to its minimum, R, right at f₀). A frequent unit trap: capacitance and inductance values in real components are usually specified in microfarads/nanofarads and millihenries, so entering raw farads and henries without converting (for example, 100 nF should be typed as 0.0000001, not 100) will shift the computed resonant frequency by orders of magnitude. This model also assumes an ideal series topology — a parallel RLC circuit has a different, complementary relationship between R, bandwidth, and Q.