RLC Impedance Calculator

Try this RLC impedance calculator to find the impedance of the resistor, capacitor, and inductor in series or in parallel.

At 20 kHz47.1587 Ωtotal impedance

Resonant frequency15.9155 kHz1 ÷ 2π√(LC) — where the two reactances cancel exactly

Inductive reactance X_L125.6637 Ωrises with frequency

Capacitive reactance X_C79.5775 Ωfalls with frequency

Net reactance46.0862 Ωinductive — above resonance

Phase angle77.757°current lags the voltage

Q factor10the sharpness of the resonance

Bandwidth1.5915 kHzf₀ ÷ Q — the width between the half-power points

Characteristic impedance √(L/C)100 Ω

Current212.05 mA

Voltage across the inductor26.647 VHIGHER than the supply — a series resonant circuit genuinely does this, by a factor of about Q, and it can destroy components rated only for the supply voltage

Voltage across the capacitor16.8744 V

Real power dissipated449.6522 mWonly the resistance dissipates — reactance stores and returns energy without loss

Power factor0.2121cos of the phase angle

At four times the capacitance7.9577 kHzhalf the frequency — f₀ goes as the inverse square root of both L and C

The formula

f₀ = 1 ÷ 2π√(LC); Z = √(R² + (X_L − X_C)²); Q = (1/R)√(L/C)

Voltages larger than the supply

Inductive reactance rises with frequency and capacitive reactance falls, so there is exactly one frequency where they cancel. At that resonance a series circuit looks purely resistive, its impedance is at a minimum, and the current is at a maximum.

The consequence that alarms people the first time they measure it: the voltage across the inductor and across the capacitor can each be far larger than the supply voltage, by roughly a factor of Q. They are equal and opposite, so they cancel as far as the source is concerned — but they are individually real, and a capacitor rated for the supply voltage will fail. This is a genuine hazard in resonant circuits, not a measurement artefact.

Q measures how sharp the resonance is, and equals √(L/C) divided by the resistance. High Q means a narrow bandwidth and large internal voltages; low Q means a broad, gentle response. Only the resistance dissipates power — reactance stores energy and gives it back, which is why a reactive load draws current without consuming energy and why power factor matters to utilities.