Understanding Realistic Inductance Values of Inductors

What Actually Determines Inductor Values

Inductors are one of those components that designers either obsess over or completely ignore. Both approaches lead to problems. The reality is that every inductor has a specific inductance value measured in henries (H), and picking the wrong one will tank your circuit performance.

Most practical circuits don't use full henries. You're looking at microhenries (μH), nanohenries (nH), and sometimes millihenries (mH). A standard 10μH inductor is nothing like a 10mH inductor—they're designed for completely different applications.

Standard Inductance Ranges You'll Actually Encounter

Here's what matters for real-world design:

• Power supply circuits: 1μH to 100μH for switching regulators, 1mH to 50mH for linear supply filtering
• RF applications: 1nH to 1000nH (1μH), sometimes down to sub-nanohenry values for microwave circuits
• Audio and signal processing: 100μH to 100mH for crossover networks and filters
• EMI/EMC filtering: 10μH to 10mH depending on the noise frequency you're targeting

If you're designing a 5V/3A buck converter, a 10μH inductor with appropriate saturation current rating is your starting point. If you're building a 100MHz RF matching network, you're looking at single-digit nanohenries—completely different ballgame.

Common Standard Values

Inductor manufacturers follow E-series standard values, just like resistors and capacitors. The E12 and E24 series are most common for through-hole inductors, while surface-mount parts often follow E12, E24, or E96.

You'll find these values readily available:

• E12 series: 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2 (and their μH/mH variants)
• E24 series adds: 1.1, 1.3, 1.6, 2.0, 2.4, 3.0, 3.6, 4.3, 5.1, 6.2, 7.5, 9.1

Factors That Actually Affect Your Inductor Choice

Core Material and Construction

The core material determines frequency response and saturation characteristics. Ferrite cores work well for 10kHz to several MHz. Iron powder cores handle DC bias better but have more losses at higher frequencies. Air-core inductors avoid saturation entirely but require more turns for the same inductance.

Your choice here affects more than just the inductance value—it affects how the inductor behaves under load, at temperature extremes, and over frequency.

DCR (DC Resistance)

This is the resistance of the wire windings. Lower DCR means less power loss and better efficiency, but it usually means larger wire or more copper. A 10μH inductor might have DCR ranging from 5mΩ to 200mΩ depending on the current rating.

For a 3A buck converter, you can't ignore DCR. 100mΩ at 3A means 0.9W of heat just from the inductor resistance. That's not trivial in a closed enclosure.

Saturation Current Rating

This is the current where the inductance drops to a specified percentage of its nominal value—usually 70-80% of nominal. Design your circuit so peak current stays below this rating. Going over saturation turns your inductor into a resistor with extra steps.

Self-Resonant Frequency (SRF)

Every inductor has parasitic capacitance between turns. This creates a resonant frequency where the inductor's impedance peaks and then drops. Above SRF, your inductor stops behaving like an inductor and starts acting like a capacitor.

For switching applications, pick an inductor with SRF at least 10x your switching frequency. For RF work, SRF becomes critical—your target frequency must stay well below it.

Comparing Inductor Types by Application

Getting Started: Picking the Right Inductance Value

Don't guess. Use the formulas that actually work:

For Switching Power Supplies

The basic buck converter inductor formula gives you a starting point:

L = (Vin - Vout) × D / (f × ΔI)

Where:

• Vin = input voltage
• Vout = output voltage
• D = duty cycle (Vout/Vin for buck)
• f = switching frequency
• ΔI = desired ripple current (typically 20-40% of output current)

Calculate your L, then round up to the nearest standard value. Then check saturation current—this is where beginners fail. Your calculated L value means nothing if the inductor saturates at your operating current.

For EMI Filtering

Target the frequency you need to attenuate. Use:

f = 1 / (2π × √(L × C))

Pick L based on your target impedance and available C values. For common-mode filtering at 150kHz-30MHz, values in the 1mH-10mH range are typical.

For RF Applications

You need Q factor and self-resonance more than precise L tolerance. Start with your impedance requirements and work backwards. A network analyzer or VNA makes this practical—trying to calculate RF inductors by formula alone is a recipe for disappointment.

What Manufacturers Get Wrong (And How to Compensate)

Part datasheets lie by omission. The inductance value is measured at a specific frequency and current. Run the inductor at different conditions and you get different results.

Common spec sheet games:

• Saturation current measured at 25°C, but your circuit runs at 85°C
• SRF specified without load, but your circuit applies DC bias
• Tolerance listed as ±20% or ±30% for many inductors—worse than most resistors
• DCR specified as typical, not maximum—actual production units may be higher

Always derate. If you need 2A saturation current, specify an inductor rated for 3A minimum. If you need ±10% tolerance, buy parts rated at ±5% or specify the tighter tolerance explicitly.

The Short Version

Realistic inductance values depend entirely on your application. Power circuits live in the 1μH to 100μH range for switching supplies, 1mH to 50mH for filtering. RF work demands nanohenries to low microhenries. Audio crosses everything in between.

Stop treating inductance as a number on a datasheet. It's a specification that changes with frequency, current, temperature, and time. Pick your inductor based on the complete picture—saturation current, DCR, SRF, and thermal performance—not just the henry value.