Inductor Reactance Calculator
Enter any two of frequency, inductance, or inductive reactance, the third is calculated instantly. Formula: XL = 2πfL.
Last updated: May 2026
Enter frequency and inductance to get XL, or any other pair to solve the missing value.
XL = 2πfL, enter f and L to get XL, or any other pair
Inductive reactance, formula and use
Inductive reactance XL is the opposition an inductor presents to alternating current at a given frequency. Unlike resistance, it scales linearly with frequency: double the frequency and the reactance doubles. This makes inductors effective as frequency-selective elements in filters, chokes and tuned circuits. Reactance is one piece of the AC picture; the companion capacitor and impedance tools in the Electronics Hub let you finish the calculation once you have this value.
Formula reference
| Solve for | Formula | Example |
|---|---|---|
| XL (Ω) | XL = 2π × f × L | f = 1 kHz, L = 10 mH → XL = 62.83 Ω |
| f (Hz) | f = XL ÷ (2π × L) | XL = 62.83 Ω, L = 10 mH → f = 1 kHz |
| L (H) | L = XL ÷ (2π × f) | XL = 62.83 Ω, f = 1 kHz → L = 10 mH |
Typical use cases
- Choosing an inductor value for an LC low-pass or high-pass filter
- Calculating the impedance of a power-supply choke at mains frequency (50/60 Hz)
- Checking whether an inductor will block high-frequency interference
- Designing RF inductors where reactance must match a target impedance
How inductors oppose AC: rising reactance with frequency
This calculator sits inside the AC sub-chain of the Electronics Hub, alongside the capacitor reactance calculator and the impedance calculator. You are here: inductive reactance (XL), the AC resistance an inductor contributes to a circuit at a given frequency. The capacitor reactance tool covers the other reactive element, XC = 1/(2pfC), which falls as frequency rises while XL climbs. Once you have both reactance values, the impedance calculator combines them with any series resistance into a single Z figure you can take back to the DC chain tools, such as the Ohm's Law calculator, to find the resulting current or voltage drop. The core behaviour worth keeping in mind: an inductor resists a change in current. Every time the AC cycle tries to reverse the current direction, the inductor's magnetic field pushes back. The higher the frequency, the more often that reversal happens and the harder the pushback, so XL = 2pfL rises in direct proportion to frequency. That is the mirror image of a capacitor, which resists a change in voltage and whose reactance falls as frequency rises. Understanding both is what lets you place a component on the right side of a filter cutoff point.
Frequently Asked Questions
What is the difference between reactance and impedance?
Reactance (X) is the opposition to AC current due to energy storage, in an inductor it is XL = 2πfL, in a capacitor XC = 1/(2πfC). Impedance (Z) is the combined opposition from both resistance (R) and reactance (X): Z = √(R² + X²). A pure inductor with no winding resistance has only reactance. Real inductors have both, use the Impedance Calculator to combine them.
Why does reactance increase with frequency?
An inductor stores energy in its magnetic field. The faster the current changes (higher frequency), the stronger the back-EMF the inductor generates to oppose that change. The mathematical result is XL = 2πfL, reactance is proportional to frequency. This is why inductors are used as high-frequency chokes: at DC and low frequencies they present little opposition; at high frequencies they block current effectively.
How do I find inductance from a given reactance and frequency?
Rearrange XL = 2πfL to L = XL / (2πf). Enter the target reactance in the XL field and the operating frequency, and the calculator returns the required inductance. This is useful when designing a filter with a specific impedance characteristic, you know the required reactance from the filter topology and need to find the inductor value.
How do I choose an inductor to block a specific switching frequency in a power supply?
Start with the switching frequency, often 50 to 500 kHz in a typical DC-DC converter, and the minimum reactance you need to keep ripple current within spec. Rearranging the reactance formula gives inductance equal to the target reactance divided by 2 pi times the frequency: enter the target reactance and the switching frequency, and the calculator returns the required inductance. A common rule of thumb is to target a reactance at least five to ten times the load impedance at the switching frequency. Also check the inductor's saturation current rating against the peak load current: a core that saturates loses most of its inductance and the ripple suppression collapses.
Methodology and sources
This tool computes inductive reactance from the standard AC-circuit relationship XL = 2πfL, and algebraically rearranges the same equation to solve for frequency or inductance when you supply the other two values.
- Method: XL = 2 × π × f × L. Rearranged, f = XL / (2 × π × L) and L = XL / (2 × π × f). Inputs are first normalised to SI base units (Hz and henries) before the calculation.
- Standards and sources: standard AC circuit theory (electromagnetic induction). There is no industry safety standard behind this figure; it is a direct application of the reactance formula with the exact constant 2π, not a tabulated or de-rated value.
- Assumptions and limits: assumes an ideal inductor with negligible winding resistance and no core losses. Real inductors add series resistance and have a self-resonant frequency above which they behave capacitively, so the reactance value is accurate only well below that point. For the total opposition of a real coil, combine reactance with resistance using the impedance tool.
Reviewed and maintained by Rick Oosterling, who builds and wires 12 V, solar and EV systems hands-on. Last reviewed: June 2026. This calculator is an informational planning aid, not a substitute for measured component data or the manufacturer's datasheet.
Next step in this workflow
Inductive reactance known: now calculate the full circuit impedance.