Reactance and Impedance Calculator (XL, XC and Z)
By Santaji GadepatilinUpdated October 27, 2026
In AC circuits, inductors and capacitors oppose current in a way that depends on frequency — this is reactance. Combined with resistance it gives impedance and a phase shift between voltage and current, as explained in impedance and reactance in AC circuits and phase angle in AC circuits. This free reactance and impedance calculator solves for whichever value you leave blank and shows the formula and steps.
How to use the reactance and impedance calculator
Enter the frequency, inductance, capacitance and series resistance. You get both reactances, the total impedance of the series RLC circuit and the phase angle. Set L or C to zero to analyse an RC or RL circuit (for an RL circuit, set C very large).
Reactance and impedance formulas
| Quantity | Formula |
|---|---|
| Inductive reactance | XL = 2πfL |
| Capacitive reactance | XC = 1 ÷ (2πfC) |
| Series impedance | Z = √(R² + (XL − XC)²) |
| Phase angle | φ = atan((XL − XC) ÷ R) |
Reactance vs frequency
| Frequency | XL of 100 mH | XC of 100 µF |
|---|---|---|
| 10 Hz | 6.28 Ω | 159.15 Ω |
| 50 Hz | 31.42 Ω | 31.83 Ω |
| 60 Hz | 37.70 Ω | 26.53 Ω |
| 100 Hz | 62.83 Ω | 15.92 Ω |
| 1000 Hz | 628.32 Ω | 1.59 Ω |
| 10000 Hz | 6283.19 Ω | 0.16 Ω |
Current in an AC circuit
Ohm’s law works with impedance: I = V ÷ Z. With 230 V across the default circuit, the current is 230 ÷ Z.
Power factor
For a series circuit, power factor = cos φ = R ÷ Z. Inductive loads such as motors have lagging power factor; capacitors are added to correct it — see the kVA to kW converter.
Applications
- Filters: reactance changes with frequency, letting RC and LC circuits pass or block certain frequencies.
- Motors and transformers: their inductance limits current and sets power factor.
- Speaker crossovers: inductors send bass to woofers; capacitors send treble to tweeters.
Frequently asked questions
What is inductive reactance?
The opposition of an inductor to AC current, XL = 2πfL. It rises with frequency.
What is capacitive reactance?
The opposition of a capacitor to AC current, XC = 1 ÷ (2πfC). It falls with frequency.
What does the phase angle mean?
Positive means the circuit is inductive (current lags voltage); negative means capacitive (current leads voltage).
When is impedance lowest?
At resonance, when XL = XC. The impedance then equals R alone. See the resonant frequency calculator.