Inductor Reactance Calculator — X_L = 2πfL | Ω to kΩ
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Enter the inductance value — select the unit (mH, H, or µH) in the next field
Enter the AC frequency — select the unit (Hz, kHz, or MHz) in the next field
Overview
The Inductor Reactance Calculator estimates ideal inductive reactance from inductance and frequency using the fixed relation X_L = 2πfL. It is useful for quick AC screening when you want to know the magnitude of an inductor's opposition to current at a given frequency.
Inductive reactance is the frequency-dependent opposition an inductor presents to alternating current. Unlike resistance, reactance increases directly with both frequency and inductance — doubling either one doubles the reactance. This calculator converts input units automatically: inductance can be entered in H, mH, or µH, and frequency in Hz, kHz, or MHz. Results are displayed in Ω for values below 1000 Ω and in kΩ for values at or above that threshold.
At DC (0 Hz), ideal inductive reactance is exactly 0 Ω. Reactance should always be compared with the surrounding circuit impedance to judge practical impact — the same value can be significant in one circuit and negligible in another.
Use this tool as a first-pass reactance screening estimate. The result is based on the ideal X_L = 2πfL formula and does not account for winding resistance, parasitic capacitance, self-resonant frequency (SRF), core loss, or real-component behavior. Final inductor selection should always be based on measured impedance curves, manufacturer data, and full circuit analysis.
How to Use This Calculator
Enter the inductance value — the inductance of the inductor you are evaluating.
Select the inductance unit — H (Henry), mH (Millihenry), or µH (Microhenry). The calculator converts to henries internally before evaluating.
Enter the frequency value — the AC frequency at which you want to evaluate the reactance.
Select the frequency unit — Hz (Hertz), kHz (Kilohertz), or MHz (Megahertz). The calculator converts to hertz internally.
Click Calculate to get the inductive reactance.
Review the result and compare it with the surrounding circuit impedance to assess the level of AC opposition at the entered frequency.
This calculator estimates ideal inductive reactance only. It does not calculate resistance, full impedance magnitude, Q factor, SRF, or core loss. For final design, compare the result with the surrounding circuit impedance and validate against manufacturer data.
Inputs & Outputs
Inputs
- •Inductance
- •Inductance Unit — Options: mH (Millihenry), H (Henry), µH (Microhenry)
- •Frequency
- •Frequency Unit — Options: Hz (Hertz), kHz (Kilohertz), MHz (Megahertz)
Outputs
- •Inductive Reactance (Ω)
Formula
Calculator Formula
This calculator uses one fixed formula for inductive reactance.
Inductive Reactance
X_L = 2πfL
Where:
- X_L = inductive reactance, Ω
- f = frequency, Hz
- L = inductance, H
- π = 3.141592653589793
Unit Conversion
Inductance and frequency are converted to SI units before calculation:
| Input Unit | Conversion to SI |
|---|---|
| H | Use directly |
| mH | L(H) = L(mH) / 1,000 |
| µH | L(H) = L(µH) / 1,000,000 |
| Hz | Use directly |
| kHz | f(Hz) = f(kHz) × 1,000 |
| MHz | f(Hz) = f(MHz) × 1,000,000 |
Display Formatting
The result is displayed in the most readable unit:
| Condition | Display Unit |
|---|---|
| X_L < 1000 Ω | Ω |
| X_L ≥ 1000 Ω | kΩ |
What is Inductive Reactance?
Inductive reactance is the frequency-dependent opposition an inductor presents to alternating current. Unlike resistance, which dissipates energy as heat, reactance stores and releases energy in the magnetic field of the inductor. The standard formula is X_L = 2πfL, where X_L is the inductive reactance in ohms, f is the frequency in hertz, and L is the inductance in henries.
Reactance is zero at DC (0 Hz) and increases linearly with frequency. This behavior is fundamental to how inductors work as filters, chokes, and impedance-shaping elements in AC circuits. In practical applications, inductive reactance is usually one part of the full impedance magnitude, which also includes winding resistance and parasitic effects. The reactance formula gives the ideal opposition — real behavior depends on the specific component, operating conditions, and circuit context.
How Frequency and Inductance Drive Reactance
Reactance increases directly with frequency because frequency appears linearly in the formula. If frequency doubles, reactance doubles. This means an inductor that has LOW reactance at 50 Hz may shift to MODERATE or HIGH reactance at 500 Hz without any change in the component itself. Understanding this linear relationship helps engineers select the right inductance for a target reactance at a given operating frequency.
Reactance also increases directly with inductance for the same reason. Doubling inductance doubles reactance. In practice, designers use both variables together to achieve a target reactance: a larger inductance reaches the same X_L at a lower frequency, while a smaller inductance can achieve it at a higher frequency. The two variables are fully interchangeable in the formula, which gives flexibility in component selection.
Reactance should always be compared with the surrounding circuit impedance to judge practical impact. A result of 10 Ω may be significant in a 5 Ω source-impedance circuit and negligible in a 10 kΩ load circuit. Interpretation is always relative to the rest of the system.
Who Uses This Calculator
This tool is useful for electrical engineers, electronics engineers, RF circuit designers, power electronics engineers, and engineering students working on inductor screening, filter design review, impedance shaping, choke selection, or first-pass reactance comparison. It is most helpful early in the design process, before detailed simulation or component testing — as a quick magnitude check to confirm that the selected inductance and operating frequency produce a reactance in the expected range.
Key Facts
- Reactance is linear in both frequency and inductance — doubling either one doubles X_L.
- At DC (0 Hz), ideal inductive reactance is exactly 0 Ω.
- Reactance alone does not determine real filter performance.
- Unit mistakes such as mH vs µH or kHz vs Hz can create 1000× errors.
- Combined inductance and frequency unit mistakes can create 1,000,000× errors.
Applications
- EMI filtering and line chokes
- AC current limiting
- Impedance shaping networks
- Resonant circuits with capacitors
- Power supply filtering
- Radio frequency (RF) circuit design
Example Calculation
Example Calculation
Example 1:
Input values:
- Inductance = 10 mH
- Frequency = 50 Hz
Convert inductance:
- L = 10 × 0.001 = 0.01 H
Calculate reactance:
- X_L = 2π × 50 × 0.01
- X_L ≈ 3.14 Ω
Result:
- Inductive Reactance = 3.14 Ω
Interpretation: The inductor offers modest AC opposition at 50 Hz. Whether 3.14 Ω is significant depends on the surrounding circuit impedance — it is small relative to a 100 Ω load but comparable to a 5 Ω source impedance.
Example 2:
Input values:
- Inductance = 100 mH
- Frequency = 1 kHz
Convert inputs:
- L = 100 × 0.001 = 0.1 H
- f = 1 × 1000 = 1000 Hz
Calculate reactance:
- X_L = 2π × 1000 × 0.1
- X_L ≈ 628.32 Ω
Result:
- Inductive Reactance = 628.32 Ω
Interpretation: The inductor presents substantial AC opposition at 1 kHz. Compare this value with source, load, and any series or parallel resistance in the circuit to assess its practical impact on current flow and voltage drop.
Standards & References
- IEC 60289 — Reactors
- IEC 62025-1 — High frequency inductive components — Fixed, surface mounted inductors for use in electronic and telecommunication equipment
- TDK — The Basics of Inductors, Part 2 — Practical free reference for AC behavior, reactance, and frequency-related inductor behavior
- IEC standards provide formal reactor and inductive-component context. Final validation depends on the real component, winding resistance, parasitics, and self-resonant behavior.
Limitations
- This calculator is an ideal reactance screening tool only.
- It does: calculate ideal inductive reactance from inductance and frequency, and improve readability with automatic Ω / kΩ formatting.
- It does not: calculate resistance, full impedance magnitude, Q factor, SRF, copper loss, core loss, saturation, or replace measured impedance or full circuit analysis.
- This tool does not confirm that the inductor, circuit design, or system performance are adequate for any specific application.
Common Mistakes to Avoid
- Mixing inductance units — confusing µH, mH, and H can change reactance by 1000× or 1,000,000×. Always verify the selected inductance unit before calculating.
- Mixing frequency units — confusing Hz, kHz, and MHz can change reactance by another 1000× or 1,000,000×. Verify the frequency unit selection every time.
- Combining unit mistakes — if both inductance and frequency units are wrong, the total error multiplies. Confusing 1 mH with 1 µH and 1 kHz with 1 Hz simultaneously creates a 1,000,000× error.
- Looking at reactance without comparing circuit impedance — reactance only becomes meaningful when compared with source, load, and any series or parallel resistance in the full circuit.
- Assuming HIGH reactance guarantees good filtering — real performance also depends on winding resistance, parasitic capacitance, self-resonant behavior, and the surrounding circuit.
- Forgetting the DC case — at 0 Hz, ideal inductive reactance is zero. An inductor behaves as a short circuit at DC in the ideal model.
Frequently Asked Questions
What is the formula for inductive reactance?
Why does reactance increase with frequency?
Why does reactance increase with inductance?
What happens at 0 Hz?
When should reactance be shown in kΩ?
Can a high reactance value still behave differently in a real circuit?
What is the difference between reactance and impedance?
Frequently Used Together
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Calculate
Enter the inductance value — select the unit (mH, H, or µH) in the next field
Enter the AC frequency — select the unit (Hz, kHz, or MHz) in the next field