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Inductive Reactance Calculator

Find the reactance of an inductor in an AC circuit.

How it is calculated

The tool applies XL = 2 × π × f × L, where f is the frequency in hertz (Hz) and L is the inductance in henries (H). The answer is in ohms (Ω) and is rounded to two decimals. The engine does no unit conversion: it multiplies the numbers exactly as entered, so a value in millihenries or kilohertz must be converted to henries and hertz first or the result will be off by a factor of 1,000.

Both inputs must be greater than zero; zero, negative or empty values give no result. Reactance rises in direct proportion to frequency and to inductance, so doubling either one doubles XL. It describes an ideal inductor and ignores the winding resistance of a real coil.

Worked example

A 100 mH choke on 60 Hz mains. Convert 100 mH to 0.1 H. Then 2 × π = 6.2832, and 6.2832 × 60 = 376.99. Multiply by 0.1 H: 376.99 × 0.1 = 37.70. The result is 37.70 Ω. At 120 Hz the same coil would present twice that, about 75.40 Ω.

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Common mistakes

  • Entering millihenries or microhenries as if they were henries. 100 mH must be typed as 0.1, otherwise the answer is 1,000 times too large.
  • Entering kHz or MHz without converting to Hz. A 1 MHz signal is 1000000, not 1.
  • Using angular frequency ω (rad/s) as f. The 2π is already in the formula, so entering ω counts it twice.
  • Treating reactance as resistance. XL is in ohms but the current lags the voltage by 90°, so it cannot simply be added to a resistor value; the two combine as vectors.
  • Expecting a result at 0 Hz (DC). The tool needs a frequency above zero, and an ideal inductor has zero reactance at DC anyway.

About this calculator

Inductive reactance is the opposition an inductor presents to alternating current: Xₗ = 2πfL, where f is the AC frequency (Hz) and L is inductance (henries). Unlike resistance, reactance is frequency-dependent and doesn't dissipate energy as heat — it stores and releases it in the inductor's magnetic field, causing current to lag voltage by 90° in a purely inductive circuit.

Electrical engineers and electricians use inductive reactance to design AC circuits involving transformers, motors, chokes, and filters — for example, calculating how much an inductor will impede current at 60 Hz mains frequency versus at radio frequencies, or sizing components in crossover networks for speakers.

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Comments (1)

  • Editorial team

    This is the reactance of an ideal inductor. A real coil also has winding resistance and stray capacitance, and above its self-resonant frequency it stops behaving like an inductor at all, so the figure is trustworthy well below that point; the datasheet usually states it. To get the opposition of a coil in series with a resistor, combine the two as the square root of R squared plus X squared rather than adding them. What frequency and coil are you working with?

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