Impedance (Z) is the total opposition to alternating current in a circuit, combining resistance (R) and reactance (X). It is measured in ohms (Ω). Unlike pure resistance, impedance depends on frequency.

What is the difference between reactance and impedance?

Reactance (X) is the opposition from inductors and capacitors only — it is frequency-dependent and causes a 90° phase shift. Impedance (Z) combines reactance with resistance: Z = √(R² + X²).

What happens at resonance?

At the resonant frequency f₀ = 1/(2π√(LC)), inductive and capacitive reactances are equal and cancel out, so X = 0. The impedance equals the resistance R and the phase angle is 0°.

Can I calculate impedance with only R (no L or C)?

Yes. If you enter only R, the impedance equals R and the phase angle is 0°. This is a purely resistive circuit.

What does a negative phase angle mean?

A negative phase angle means the circuit is capacitively reactive — the current leads the voltage. A positive angle means the circuit is inductively reactive — current lags voltage.

What units does this calculator use?

Resistance in ohms (Ω), inductance in henries (H), capacitance in farads (F), and frequency in hertz (Hz). Use scientific notation (e.g. 1e-6 for 1 µF) for small values.

Impedance Calculator

Enter resistance (R), inductance (L), capacitance (C), and frequency (f) to get the total impedance, reactance, and phase angle of an RLC circuit.

Circuit Parameters

Frequency (f) Hz

Resistance (R) Ω — leave blank for 0

Inductance (L) H — leave blank to omit

Capacitance (C) F — leave blank to omit

Results

Enter values and click Calculate

Formula Reference

Inductive Reactance

X_L = 2π · f · L

Capacitive Reactance

X_C = 1 / (2π · f · C)

Net Reactance

X = X_L − X_C

Impedance

Z = √(R² + X²)

Phase Angle

θ = arctan(X / R)

Resonant Frequency

f₀ = 1 / (2π√(LC))

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Summary

This tool computes the total impedance Z of a series RLC circuit from resistance (R), inductance (L), capacitance (C), and frequency (f). It also shows inductive reactance (XL), capacitive reactance (XC), net reactance, and phase angle after you click Calculate or press Enter.

How it works

Enter the resistance R in ohms (leave L or C blank to treat them as absent).
Enter the inductance L in henries and/or capacitance C in farads.
Enter the frequency f in hertz.
The tool computes XL = 2πfL, XC = 1/(2πfC), net reactance X = XL − XC.
Total impedance Z = √(R² + X²) in ohms.
Phase angle θ = arctan(X / R) in degrees (positive = inductive, negative = capacitive).

Use cases

Design series RLC filters and resonant circuits.
Check impedance matching in audio amplifier output stages.
Calculate the impedance of a speaker crossover network.
Verify LC tank circuit behavior at a target frequency.
Study AC circuit theory and verify textbook problems.
Determine the phase relationship between voltage and current.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu