A series RLC circuit combines a resistor, inductor, and capacitor along a single current path, and how it responds depends heavily on the driving frequency. This calculator computes the three quantities engineers and students check most often: impedance (the total opposition to current at a given frequency), resonant frequency (where impedance is at its minimum), and phase angle (whether current leads or lags voltage, and by how much).
How the RLC Circuit Calculator works
The calculator first finds each reactive component's opposition to current: inductive reactance X_L = 2ΟfL grows with frequency, while capacitive reactance X_C = 1/(2ΟfC) shrinks with frequency. Because they move in opposite directions, the resistor's steady resistance R and this frequency-dependent net reactance (X_L β X_C) combine like the two legs of a right triangle to give the total impedance, Z = β(RΒ² + (X_L β X_C)Β²) β the hypotenuse. The same three quantities determine the phase angle Ο = atan((X_L β X_C)/R), the offset between the voltage and current waveforms. Separately, the resonant frequency fβ = 1/(2Οβ(LC)) is the one frequency where X_L and X_C are exactly equal β at that point they cancel completely, Ο drops to 0Β°, and impedance falls to its absolute minimum, Z = R.
Inputs and what they mean
Resistance (R) is the circuit's real, frequency-independent opposition to current, in ohms. Inductance (L) sets how strongly a changing current induces an opposing voltage β measured in henries, but usually entered in millihenries (mH) or microhenries (Β΅H) for real-world coils. Capacitance (C) sets how much charge a capacitor stores per volt β in farads, though practical capacitors are almost always specified in microfarads (Β΅F), nanofarads (nF), or picofarads (pF). Frequency (f) is the AC source's driving frequency in hertz. Of the four, L and C together set where resonance occurs; R doesn't move the resonant frequency at all, but it does set the impedance floor at resonance and how sharply impedance rises as you move away from fβ.
Limits and edge cases
This calculator models an ideal series RLC circuit with a single resistor, inductor, and capacitor β it does not account for parallel (tank) RLC topologies, parasitic resistance inside real-world inductors and capacitors, or multi-stage filter networks, all of which shift the effective resonance and damping. A resistance of exactly 0 Ξ© is accepted (an idealized LC circuit) and produces a phase angle of exactly Β±90Β° rather than an undefined result. Extremely small resistances combined with a frequency very close to resonance can make the theoretical current spike sharply β in a real circuit, parasitic resistance in the wiring and components limits how far this actually goes, so treat results very near resonance with R β 0 as a theoretical bound rather than a literal current reading.