Calculators
Reactance Calculator
Calculate capacitor or inductor reactance at an AC frequency.
Calculate ideal capacitive reactance (Xc) or inductive reactance (XL) at a chosen AC frequency. Inputs stay in your browser.
Capacitive reactance (Xc)
159.15494 Ω
Angular frequency (ω)6283.1853 rad/s
The result is the ideal reactance magnitude for a pure capacitor or inductor. Real components also have resistance, ESR, parasitics, tolerances, and frequency limits.
About This Tool
Reactance is the frequency-dependent opposition that ideal capacitors and inductors present to alternating current. Unlike resistance, reactance changes when frequency changes: capacitor reactance falls as frequency rises, while inductor reactance rises. This calculator handles both relationships in one page so you can estimate Xc or XL for filters, timing networks, AC analysis, signal paths, and electronics study. Calculations run locally in your browser.
How To Use It
- Choose Capacitive (Xc) for a capacitor or Inductive (XL) for an inductor.
- Enter the AC frequency and select Hz, kHz, MHz, or GHz.
- Enter capacitance or inductance and select the engineering unit that matches your component value.
- Read the ideal reactance magnitude in ohms and the corresponding angular frequency.
Examples
1 µF capacitor at 1 kHz
Using Xc = 1/(2πfC), a 1 µF ideal capacitor at 1 kHz has about 159.15 Ω of capacitive reactance.
10 mH inductor at 1 kHz
Using XL = 2πfL, a 10 mH ideal inductor at 1 kHz has about 62.83 Ω of inductive reactance.
Effect of doubling frequency
For the same component, doubling frequency halves ideal capacitive reactance but doubles ideal inductive reactance.
Useful Notes
Capacitive reactance formula
For an ideal capacitor, Xc = 1/(2πfC), where f is frequency in hertz and C is capacitance in farads. Xc is reported as a positive magnitude in ohms; in complex impedance a capacitor contributes a negative imaginary term.
Inductive reactance formula
For an ideal inductor, XL = 2πfL, where f is frequency in hertz and L is inductance in henries. XL is the positive reactance magnitude in ohms; in complex impedance an inductor contributes a positive imaginary term.
Why frequency matters
At higher frequency an ideal capacitor more readily passes changing current, so Xc decreases. An ideal inductor increasingly opposes changing current, so XL increases. This opposite behavior is central to filters and resonant circuits.
Reactance versus impedance
Reactance is only the imaginary part of impedance. A real circuit can also contain resistance and multiple reactive elements, so total impedance generally requires combining resistance and net reactance as complex quantities rather than treating this result as total opposition.
Real component limitations
Actual capacitors and inductors include ESR, winding resistance, parasitic capacitance or inductance, tolerances, losses, and self-resonant behavior. Near or beyond a component's self-resonant frequency, the simple ideal formula may no longer describe its measured impedance well.
Using engineering units
The calculator converts common units to SI before applying the formula. For example, 1 µF is 0.000001 F and 10 mH is 0.01 H, which helps avoid manual power-of-ten errors.
FAQ
Is reactance measured in ohms?
Yes. Reactance is measured in ohms, like resistance, but it represents the frequency-dependent imaginary part of impedance rather than dissipative resistance.
Why does capacitor reactance decrease with frequency?
The formula Xc = 1/(2πfC) places frequency in the denominator, so increasing frequency reduces ideal capacitive reactance.
Can I use this as an impedance calculator?
Not for a complete circuit. This tool calculates the ideal reactance magnitude of one capacitor or one inductor. Total impedance may also include resistance and other reactive elements.
What happens at 0 Hz?
The ideal formulas reach limiting DC behavior: capacitor reactance tends toward infinity and inductor reactance tends toward zero. This calculator requires frequency above zero because it is designed for finite AC reactance calculations.
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