Use this quick calculator to find the impedance (inductive reactance) of an inductor at a given frequency. Enter frequency and inductance, choose the proper units, and click calculate.
Inductor Impedance Calculator
Where: XL is reactance in ohms (Ω), f is frequency in hertz (Hz), and L is inductance in henries (H).
Complex impedance of an ideal inductor: Z = jXL
What is the impedance of an inductor?
In AC circuits, an inductor resists changes in current. That opposition is called inductive reactance. For an ideal inductor, impedance is purely imaginary and written as Z = jXL. The key takeaway: as frequency increases, inductor impedance increases linearly.
Core equation
The reactance of an inductor is:
XL = 2πfL
- XL = inductive reactance in ohms (Ω)
- f = frequency in hertz (Hz)
- L = inductance in henries (H)
If frequency doubles, reactance doubles. If inductance doubles, reactance doubles.
How to use this calculator
- Enter the signal frequency and choose its unit (Hz, kHz, MHz, or GHz).
- Enter inductance and choose the unit (H, mH, µH, or nH).
- Click Calculate Impedance.
- Read reactance XL, complex impedance form, and angular frequency ω.
Worked examples
Example 1: Power line inductor
Suppose L = 50 mH and f = 60 Hz. Convert L to henries: 50 mH = 0.05 H. Then: XL = 2π(60)(0.05) ≈ 18.85 Ω. So the inductor contributes roughly j18.85 Ω of impedance.
Example 2: High-frequency converter
If L = 22 µH and f = 100 kHz: L = 22 × 10-6 H and f = 100,000 Hz. XL = 2π(100,000)(22 × 10-6) ≈ 13.82 Ω.
Why this matters in real circuit design
- Filters: Inductors and capacitors shape frequency response.
- Power electronics: Reactance influences ripple current and switching behavior.
- RF circuits: Inductive reactance is central to matching networks and resonant circuits.
- Signal integrity: Inductance can help or hurt depending on operating frequency.
Important practical notes
Real inductors are not ideal. They include winding resistance, parasitic capacitance, and core losses. At very high frequency, many inductors approach self-resonance, where behavior no longer matches simple XL = 2πfL. Use datasheets and impedance-vs-frequency plots for precision work.
FAQ
Is reactance the same as resistance?
Not exactly. Resistance dissipates energy as heat. Reactance stores and releases energy (magnetic field for inductors).
What happens at DC?
At f = 0 Hz, ideal inductive reactance is 0 Ω. In steady-state DC, an ideal inductor acts like a short.
Can impedance be negative for an inductor?
For passive ideal inductors, reactance magnitude is non-negative. The imaginary sign is +j for inductive behavior.