Reactance Calculator
Pick component type, enter the value and frequency, and get the reactance in ohms — the AC 'resistance' of inductors and capacitors.
Last updated: 2026-09-28
How the calculation works
- Inductive reactance rises with frequency: Xʟ = 2πfL — an inductor passes DC and increasingly blocks AC.
- Capacitive reactance falls with frequency: X꜀ = 1/(2πfC) — a capacitor blocks DC and passes high frequencies.
- Reactance shifts phase: current lags 90° through an inductor, leads 90° through a capacitor — the basis of filters and PF correction.
Formula
Xʟ = 2π × f × L X꜀ = 1 / (2π × f × C)
| Symbol | Meaning | Unit |
|---|---|---|
X | Reactance magnitude | Ω |
f | Frequency | Hz |
L, C | Inductance / capacitance | H, F |
Worked example
Interpreting the result
Reactance is the AC resistance that sets filter corner frequencies (f = 1/2πRC or 1/2π√(LC) for LC), motor-run capacitor sizing, and choke design. It is not loss: an ideal reactance stores and returns energy each cycle, so a capacitor drawing kVARs adds little to your kWh bill — but it does load the conductors, which is why PF correction exists.
Assumptions
- Ideal components: real parts add series resistance (ESR) and self-resonance above which behavior inverts.
- Sinusoidal steady state at the stated frequency.
Limitations
- At self-resonant frequency and beyond, real inductors act capacitive (and vice versa).
- Magnetic-core inductors lose inductance with DC bias (saturation).
Frequently asked questions
What is the reactance of a capacitor at 60 Hz?
X꜀ = 1/(2π·60·C). A 10 µF capacitor shows 265 Ω; a 100 µF shows 26.5 Ω. Bigger capacitors and higher frequencies both mean lower reactance.
Is reactance the same as impedance?
Impedance is the vector sum of resistance and reactance: Z = √(R² + X²). Reactance is the imaginary part alone — no energy is lost in ideal reactance, only in the resistive part.