Inductance Calculator

Inductor Code Decoder

Enter the 3-digit or 4-digit code printed on an SMD inductor to decode its inductance value. The letter R represents a decimal point (e.g., 4R7="4.7" µH).

Core Material Comparison

Choosing the right core material is critical for inductor performance. The core determines the achievable inductance, frequency range, saturation current, and losses. Here is a comparison of the most common core materials used in electronics design.

µr="relative" permeability. Saturation flux density at 25 degrees C. Actual values depend on specific grade and manufacturer.

Inductor Types Guide

Understanding the different physical types of inductors helps you select the right component for your application. Each type has distinct advantages in terms of size, current handling, frequency response, and electromagnetic interference.

Through-Hole Inductors

Axial leaded inductors look similar to resistors and use color bands for marking. Radial leaded types include drum core, toroid, and bobbin-wound styles. Through-hole inductors handle higher currents than most SMD equivalents and are easier to prototype with. Common in power supplies, audio equipment, and hobby electronics. Typical inductance range: 1 µH to 100 mH.

SMD/SMT Inductors

Surface-mount inductors come in wire-wound, multilayer ceramic, and thin-film types. Wire-wound SMD inductors offer high current ratings and good Q factors but are physically larger. Multilayer ceramic types are very small (down to 0201 package) but have lower Q and current ratings. Thin-film inductors provide excellent tolerance and high-frequency performance for RF applications. Standard packages: 0201, 0402, 0603, 0805, 1008, 1210, 1812.

Toroidal Inductors

Toroids confine the magnetic field within the core, resulting in very low electromagnetic interference and high inductance per turn. They are the preferred choice for EMI-sensitive applications, audio equipment, and common-mode chokes. The closed magnetic path means they can achieve higher inductance with fewer turns compared to solenoid designs. they are harder to wind and cannot be manufactured on standard automated winding machines.

Shielded vs. Unshielded

Shielded inductors have a metal or ferrite enclosure that contains the magnetic field, reducing EMI radiation and susceptibility to external fields. Essential in dense PCB layouts where crosstalk between components is a concern. Unshielded inductors are less expensive and often physically smaller for the same rating, but their fringing fields can couple to nearby components and traces. For sensitive analog circuits, always use shielded inductors or toroids.

Common Inductance Values (E12 Series)

Standard preferred inductance values follow the E12 series (10% tolerance). These are the values most readily available from distributors. When designing, try to use standard values to ensure availability and lower cost.

EMI Filter Design Basics

Electromagnetic interference (EMI) is one of the most common challenges in electronics design. Inductors play a central role in EMI filtering by blocking high-frequency noise while passing desired signals or power. Understanding the fundamentals of inductor-based EMI filtering is essential for any electronics designer working with switching power supplies, digital circuits, or mixed-signal systems.

Common Mode vs. Differential Mode

Differential mode noise flows in opposite directions on the two conductors of a pair, while common mode noise flows in the same direction on both conductors and returns through ground. Differential mode filtering uses standard inductors in series with the signal path, forming LC low-pass filters with bypass capacitors. Common mode filtering requires common mode chokes, which are wound with two windings on the same core so that differential currents cancel while common mode currents add. The impedance presented to common mode noise can be very high (thousands of ohms) while the impedance to the desired differential signal is almost zero.

LC Filter Design

A simple LC low-pass filter has a cutoff frequency of f_c="1" / (2π√(LC)). Above this frequency, attenuation increases at 40 dB/decade (second-order filter). For a switching power supply operating at 500 kHz that needs 40 dB of attenuation at the fundamental switching frequency, you would need the LC cutoff to be approximately one decade below 500 kHz, so around 50 kHz. With L="10" µH, the required C="1/(4π²" × f_c² × L) = approximately 1 µF. Multi-stage LC filters provide steeper rolloff when single-stage attenuation is insufficient.

Ferrite Bead Selection

Ferrite beads are a special type of inductor specifically for EMI suppression. Unlike standard inductors, ferrite beads are characterized by their impedance at specific frequencies (typically 100 MHz) rather than their inductance. The impedance of a ferrite bead is primarily resistive at the target frequency, which means the noise energy is converted to heat rather than reflected. Select ferrite beads based on: (1) impedance at the noise frequency, (2) DC resistance and current rating, (3) impedance vs. frequency curve matching your noise spectrum. Common ratings: 30 ohms, 60 ohms, 120 ohms, 220 ohms, 600 ohms, and 1000 ohms at 100 MHz.

Practical Design Tips

Place EMI filter components as close to the noise source or entry point as possible. Keep the PCB traces between filter components short to reduce parasitic inductance and capacitance that can compromise filter performance. Use ground planes on both sides of the filter to provide a low-impedance return path. Orient inductors perpendicular to each other to reduce magnetic coupling between filter stages. Always verify filter performance with an EMI pre-scan before final compliance testing, as parasitic effects on the PCB can shift the actual filter response significantly from the calculated values.

Inductive Reactance vs. Frequency

This chart shows how inductive reactance (XL) increases linearly with frequency for three common inductance values.

Generated via quickchart.io · XL="2πfL" increases linearly with both frequency and inductance

Video Inductors Explained

An excellent visual explanation of how inductors work, covering magnetic fields, self-inductance, Lenz's law, and practical applications in circuits.

Browser Compatibility

I've tested this inductance calculator across all major browsers to ensure accurate results and proper rendering. All calculations use standard JavaScript Math functions with full cross-browser support.

Frequently Asked Questions