AC impedance tool
Reactance calculator
Calculate ideal inductive or capacitive reactance at a selected frequency. You can also work backward from a target reactance to find the required inductance, capacitance, or frequency.
Calculated reactance
Ideal impedance
+j62.8319 Ω
+90° phase
Reactance magnitude
62.8319 Ω
Frequency
1 kHz
Inductance
10 mH
Angular frequency
6.2832 krad/s
Ideal susceptance
−j15.9155 mS
Ideal component result
Reactance is the imaginary part of impedance; it does not include ESR, winding resistance, leakage, or parasitic resonance.
Ideal reactance across frequency
Inductive reactance rises in direct proportion to frequency.
Log frequency and reactance scales
How to use the reactance calculator
Choose the ideal component model and the quantity you need to calculate, then enter positive values in convenient engineering units.
- 01
Choose an inductor or capacitor
Inductive reactance increases with frequency, while capacitive reactance decreases as frequency rises.
- 02
Choose what to calculate
Calculate reactance directly, solve for the component value that gives a target reactance, or solve for the required frequency.
- 03
Review the ideal result and trend
Use the complex impedance, phase, susceptance and frequency curve as ideal references, then compare them with the component datasheet or measurement.
Inductive and capacitive reactance equations
The calculator uses ideal sinusoidal steady-state relationships and reports reactance magnitude as a positive value while preserving the impedance sign separately.
Inductive reactance
XL = 2πfL
Capacitive reactance magnitude
|XC| = 1 / (2πfC)
Ideal complex impedance
ZL = +jXL; ZC = −j|XC|
Inductance for a target reactance
L = XL / (2πf)
Capacitance for a target reactance
C = 1 / (2πf|XC|)
Frequency from reactance
f = XL / (2πL) or 1 / (2πC|XC|)
For an ideal inductor, impedance has a positive imaginary term and voltage leads current by 90 degrees. For an ideal capacitor, impedance has a negative imaginary term and voltage lags current by 90 degrees. Susceptance is the imaginary part of admittance and therefore has the opposite sign for an ideal inductor and a positive sign for an ideal capacitor.
Real inductors and capacitors include resistance, leakage, parasitic capacitance or inductance, and self-resonance. Their effective impedance also depends on frequency, signal level, DC bias, temperature, package, mounting and the measurement fixture. Use the ideal result as a first calculation and verify critical behavior with the component datasheet or an impedance measurement.
Practical reactance checks
Reactance is frequency-dependent, so component selection requires more than matching a single calculated value.
Use the relevant frequency spectrum
For switching edges, pulses and non-sinusoidal waveforms, evaluate important harmonics rather than checking only the repetition or fundamental frequency.
Do not confuse reactance with total impedance
Reactance is the imaginary part of impedance. ESR, winding resistance and other real losses change both impedance magnitude and phase.
Check self-resonant frequency
A real capacitor can become inductive above resonance, and a real inductor can become capacitive. Avoid extrapolating the ideal trend beyond the useful frequency range.
Match datasheet and measurement conditions
Test frequency, AC level, DC bias, fixture compensation and temperature can change the measured capacitance, inductance and impedance.
Reactance calculator questions
What is the difference between resistance and reactance?
Resistance is the real component of impedance and dissipates energy in the ideal model. Reactance is the imaginary component associated with energy storage in electric or magnetic fields.
Why is capacitive reactance negative?
The negative sign identifies the capacitive impedance phase in complex notation. The calculator displays a positive magnitude for convenience and shows the full ideal impedance as −jX.
Why does inductive reactance increase with frequency?
The ideal relationship XL = 2πfL is directly proportional to frequency, so doubling frequency doubles the inductive reactance for a fixed inductance.
Why does capacitive reactance decrease with frequency?
The ideal relationship |XC| = 1/(2πfC) is inversely proportional to frequency, so doubling frequency halves the capacitive reactance for a fixed capacitance.
Is the calculated reactance the same as measured impedance?
Only for an ideal component with no loss or parasitic effects. A real measurement includes resistance and additional frequency-dependent behavior, so magnitude and phase can differ from the ideal result.
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