An axial molded inductor uses a 4-band colour code to specify its inductance value in microhenries (µH). The first two bands represent significant digits, the third is the multiplier, and the fourth indicates tolerance. Unlike resistors, which are read in ohms, the baseline unit for the standard inductor colour code is always microhenries unless explicitly marked otherwise on the component body.
The Standard Inductor Colour Code Chart
The following table follows the IEC 60062 (formerly EIA) standard for passive component marking. Read the bands from left to right, starting from the band closest to the lead wire.
| Band Colour | 1st Digit (Band 1) | 2nd Digit (Band 2) | Multiplier (Band 3) | Tolerance (Band 4) |
|---|---|---|---|---|
| Black | 0 | 0 | x1 (10^0) | — |
| Brown | 1 | 1 | x10 (10^1) | ±1% (Rare) |
| Red | 2 | 2 | x100 (10^2) | ±2% (Rare) |
| Orange | 3 | 3 | x1,000 (10^3) | ±3% |
| Yellow | 4 | 4 | x10,000 (10^4) | ±4% |
| Green | 5 | 5 | x100,000 (10^5) | — |
| Blue | 6 | 6 | — | — |
| Violet | 7 | 7 | — | — |
| Grey | 8 | 8 | x0.1 (10^-1) | — |
| White | 9 | 9 | — | — |
| Gold | — | — | x0.1 (10^-1) | ±5% |
| Silver | — | — | x0.01 (10^-2) | ±10% |
Example: A molded choke with Brown (1), Black (0), Red (x100), and Gold (±5%) bands equals 10 x 100 = 1,000 µH (or 1 mH) with a 5% tolerance.
Rows People Get Wrong (And How to Fix Them)
Even experienced bench technicians misread inductors when they apply resistor logic blindly. Here are the specific rows and scenarios that cause errors:
1. The Gold and Silver Multiplier Trap
In resistor codes, gold and silver only appear in the tolerance band or as decimal multipliers for very low ohm values. In the inductor colour code, gold (x0.1) and silver (x0.01) are frequently used as the third band multiplier for RF chokes. If you see Brown-Black-Gold-Gold, it is not 10 ohms; it is 1.0 µH (10 x 0.1) with a ±5% tolerance. Always verify if the third band is a metallic colour before assuming it is the tolerance band.
2. The Missing Tolerance Band (3-Band Inductors)
Cheap, mass-produced radial and axial RF chokes often only have three colour bands. If your inductor lacks a fourth band, the default tolerance is ±20%. Do not assume the third band is the tolerance; in a 3-band system, the third band is always the multiplier, and the ±20% tolerance is implied by the manufacturer.
3. Confusing Microhenries with Millihenries
The standard IEC 60062 colour code outputs the value in microhenries (µH). A common mistake is reading a 470 µH inductor (Yellow-Violet-Brown) and assuming the output is in millihenries. If you need millihenries, you must manually divide the colour code result by 1,000. For authoritative passive component theory, refer to the Electronics Tutorials inductor guide.
Regional Standards, MIL-SPEC Variants, and Faded Markings
While IEC 60062 is the global baseline for commercial and hobbyist electronics, you will encounter different standards in specialized equipment.
MIL-PRF-39010 and Aerospace Dot Codes
If you are repairing military, aerospace, or vintage telecommunications gear, you may find molded RF inductors marked with a completely different system. The US Military Specification MIL-PRF-39010 uses a numeric stamp or a multi-dot colour code rather than the standard 4-band EIA stripes. These components often mark values in nanohenries (nH) rather than microhenries. If the component has a 'M' prefix stamped on the body, abandon the standard colour chart and look up the specific MIL-SPEC datasheet.
Safe Interpretation When Markings are Faded or Missing
Molded inductors run hot. Over years of thermal cycling in power supplies or audio crossovers, the epoxy coating yellows, and the colour bands fade into illegibility. Never guess the value of a faded inductor based on its physical size; core permeability and winding density vary wildly between manufacturers.
Bench Rule: If the colour code is compromised, you must measure it. Desolder at least one leg of the inductor to isolate it from the circuit's parallel capacitance and resistance, then use an LCR meter.
When using an LCR meter (like a Der EE DE-5000 or Uni-T UT612), test frequency matters. According to Georgia State University's HyperPhysics magnetic principles, inductance varies with frequency due to core losses and parasitic capacitance. Use these bench settings:
- Values > 100 µH: Test at 100 Hz or 120 Hz (matches mains ripple frequencies).
- Values 10 µH to 100 µH: Test at 1 kHz (the standard EIA reference frequency).
- Values < 10 µH (RF Chokes): Test at 100 kHz or 1 MHz to get an accurate reading of high-frequency behaviour.
Inductor Colour Code FAQ
How do I read a 3-band inductor colour code?
Read the first two bands as significant digits and the third band as the multiplier, exactly as you would with a 4-band inductor. The only difference is that a 3-band inductor lacks a dedicated tolerance band. By industry convention, if the fourth band is missing, the tolerance defaults to ±20%. For example, Red-Violet-Black translates to 27 x 1 = 27 µH (±20%).
Is the inductor colour code the same as the resistor colour code?
The colour-to-number mapping (Black=0, Brown=1, Red=2, etc.) is identical to the resistor colour code. However, the base unit is different. Resistor codes output in Ohms (Ω), while the standard inductor colour code outputs in microhenries (µH). Additionally, inductors frequently use gold and silver as the third-band multiplier for sub-microhenry RF values, which is rare in standard through-hole resistors.
What does a double-width band mean on an axial inductor?
If you see a single band that is roughly twice as wide as the others, usually located at the far left or right end of the component body, it indicates a specific manufacturer's proprietary marking or a military-spec reliability grade. In some vintage Japanese EIAJ standards, a double-width first band indicates a specific core material (like ferrite vs. powdered iron). If you encounter a double-width band, do not rely on the standard IEC chart; measure the component with an LCR meter to confirm its actual value.
Can I use a standard multimeter to read an inductor's value?
No. A standard digital multimeter (DMM) measures DC resistance, not inductance. If you put a DMM in resistance mode across an inductor, you will only read the DC resistance (DCR) of the copper wire windings, which is usually less than 5 ohms. To measure the actual inductance value dictated by the colour code, you must use a dedicated LCR meter or an oscilloscope with a function generator to measure the resonant frequency of an LC tank circuit.
