Inductive Reactance Calculator – XL Formula, Free Online

How to use the inductive reactance calculator

1. Enter the frequency (f) in hertz — for example, 50 for mains frequency or 1000 for a 1 kHz signal.
2. Enter the inductance (L) in henrys — most small coils are labelled in millihenrys (mH) or microhenrys (µH), so convert first: 100 mH is 0.1 henrys.
3. Click “Calculate Reactance”.
4. Read the result in ohms, shown on the page.

A worked example

Take a 100 mH inductor — that is 0.1 henrys — in a 50 Hz mains circuit. The formula is XL = 2 × π × f × L, so 2 × π × 50 × 0.1 = 31.42. The inductive reactance is about 31.4 ohms. Run the same inductor at 1,000 Hz and the answer becomes 628 ohms, twenty times larger. That is the defining behaviour of inductors: higher frequency means higher reactance, the exact opposite of a capacitor. At direct current, zero frequency, an ideal inductor offers no reactance at all — only the resistance of its wire remains.

When inductive reactance matters

• Power and mains circuits: transformers, motors and chokes all present reactance at 50 or 60 Hz, and XL is part of working out their total impedance and current draw.
• Filters and crossovers: inductors block high frequencies and pass low ones, so XL decides where a low-pass filter or a speaker crossover starts to cut in.
• Radio and tuning circuits: paired with a capacitor, an inductor sets a resonant frequency — the basis of radio tuning, which the LC resonance calculator works out for you.
• Electronics study: textbook problems almost always give frequency and inductance and ask for XL, or give XL and frequency and ask for the inductance.

What the result means

Like capacitive reactance, inductive reactance is measured in ohms but is not resistance: an ideal inductor stores energy in its magnetic field and returns it, rather than turning it into heat. It also shifts the timing of the current, but in the opposite direction to a capacitor — current lags voltage in an inductor, while it leads in a capacitor. That opposite shift is why a capacitor and an inductor in the same circuit can cancel each other’s reactance at one special frequency, the resonant frequency, where the circuit behaves as if neither were there.

Honest limitations

• The calculator assumes an ideal inductor. Real coils have wire resistance and stray capacitance, which matter at high frequencies and for precise work.
• Watch your units: entering 100 instead of 0.1 for a 100 mH coil gives an answer a thousand times too large, so convert millihenrys and microhenrys to henrys first.
• The result is for one steady frequency. Real signals contain many frequencies, each with its own reactance.
• This tool gives XL only. For the total impedance of a resistor-inductor circuit, combine resistance and reactance with Z = √(R² + XL²).

Inductive reactance calculator – frequently asked questions

What is the formula for inductive reactance?

XL = 2πfL, where f is the frequency in hertz and L is the inductance in henrys. The answer comes out in ohms.

Does reactance go up or down with frequency?

Up. Doubling the frequency doubles the reactance. At zero frequency, direct current, an ideal inductor has zero reactance.

What units should I enter?

Frequency in hertz and inductance in henrys. Divide millihenrys by 1,000 and microhenrys by 1,000,000 to get henrys.

How is it different from capacitive reactance?

They move in opposite directions with frequency, and they shift current timing in opposite directions too. Compare with the capacitive reactance calculator to see both behaviours side by side.