inductor impedance calculator

What Is Inductor Impedance?

Inductor impedance is the opposition an inductor presents to alternating current (AC). Unlike a resistor, which blocks current equally at all frequencies, an inductor blocks more current as frequency increases. This behavior is called inductive reactance.

In a real circuit, an inductor is rarely perfect. Most coils have some copper resistance (often called DCR), so total impedance is a combination of:

• Resistance (R) from wire and core losses
• Reactance (X_L) caused by inductance and frequency

Core Formula for Inductive Reactance

The most important equation is:

X_L = 2πfL

• X_L = inductive reactance in ohms (Ω)
• f = frequency in hertz (Hz)
• L = inductance in henries (H)

If resistance is included, impedance becomes complex:

Z = R + jX_L

Magnitude:

|Z| = √(R² + X_L²)

How to Use This Calculator

1) Enter Inductance

Type the coil value and select H, mH, µH, or nH. The calculator converts everything to henries internally.

2) Enter Frequency

Type the signal frequency and choose Hz, kHz, MHz, or GHz. Reactance changes directly with frequency.

3) Add Series Resistance (Optional)

If your inductor has measurable DCR, enter it for realistic impedance magnitude and phase angle.

4) Click Calculate

You will get reactance, complex impedance, magnitude, phase angle, and quality factor (Q).

Worked Example

Suppose you have a 10 mH inductor at 1 kHz with 0.5 Ω series resistance.

• X_L = 2π(1000)(0.01) = 62.83 Ω
• Z = 0.5 + j62.83 Ω
• |Z| ≈ 62.83 Ω (resistance is small compared with reactance)
• Phase angle ≈ +89.54°

This shows why inductors are often used to block high-frequency components while passing lower-frequency or DC components.

Why Frequency Matters So Much

At DC (0 Hz), ideal inductor reactance is 0 Ω, so the inductor behaves like a short circuit. As frequency rises, reactance rises linearly. Doubling frequency doubles reactance; increasing frequency by 10x increases reactance by 10x.

This frequency dependence is fundamental in:

• Filters (low-pass, high-pass, band-pass)
• Switching power supplies
• RF matching networks
• EMI suppression and chokes

Ideal vs Real Inductors

Ideal Inductor

• No winding resistance
• No core losses
• No parasitic capacitance
• Phase angle exactly +90°

Real Inductor

• Has DCR (copper resistance)
• Core losses at higher frequencies
• Self-resonant frequency due to parasitic capacitance
• Phase angle below +90°

For high-frequency work, always check the inductor datasheet for Q, ESR, and self-resonance behavior.

Common Unit Conversions

• 1 H = 1000 mH
• 1 mH = 1000 µH
• 1 µH = 1000 nH
• 1 kHz = 1000 Hz
• 1 MHz = 1,000,000 Hz

Practical Design Tips

• Use the calculator early when selecting choke and filter values.
• Include DCR for power circuits where loss and heat matter.
• For RF design, check impedance across a frequency sweep, not one point.
• Keep inductor tolerance in mind (e.g., ±10%) when estimating worst-case behavior.

Quick FAQ

Does higher inductance always mean higher impedance?

At a fixed frequency, yes. Since X_L = 2πfL, increasing L increases reactance proportionally.

Can impedance be zero?

For an ideal inductor at DC, reactance is zero. Real inductors still have winding resistance, so practical impedance is usually not exactly zero.

What does j mean in impedance?

j represents the imaginary axis in complex numbers. It indicates phase shift between voltage and current in AC circuits.