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 any two values above to calculate the third.
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.
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
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.
What units should I use for frequency and inductance?
The formula uses SI base units: frequency in Hz and inductance in henries (H). Use the unit selector to work in kHz/MHz or mH/µH/nH — the calculator converts automatically. Common practical values: power-supply chokes are in the mH range at 50/60 Hz; RF inductors for the HF band (3–30 MHz) are typically 0.1–10 µH.
Next step in this workflow
Inductive reactance known: now calculate the full circuit impedance.