The standard color code for inductors uses the EIA 4-band system, visually identical to the resistor color code, but with one critical difference: the base unit of measurement is microhenries (µH), not ohms. While resistors measure resistance to current flow, inductors store energy in a magnetic field, and their physical size usually dictates values in the µH range rather than full Henries. If you are looking at a standard axial or molded through-hole choke, read the bands from left to right (or from the end where the bands are grouped closest to the lead) to find your inductance and tolerance.
The Standard EIA Inductor Color Code Reference Chart
The table below contains the complete EIA (Electronic Industries Alliance) standard values for 4-band inductors. Keep this bookmarked for bench work. The first two bands represent significant digits, the third band is the multiplier, and the fourth band indicates the manufacturing tolerance.
| Color | 1st Band (Digit) | 2nd Band (Digit) | 3rd Band (Multiplier) | 4th Band (Tolerance) |
|---|---|---|---|---|
| Black | 0 | 0 | 1 (x1) | — |
| Brown | 1 | 1 | 10 | — |
| Red | 2 | 2 | 100 | — |
| Orange | 3 | 3 | 1,000 | — |
| Yellow | 4 | 4 | 10,000 | — |
| Green | 5 | 5 | — | — |
| Blue | 6 | 6 | — | — |
| Violet | 7 | 7 | — | — |
| Gray | 8 | 8 | — | — |
| White | 9 | 9 | — | — |
| Gold | — | — | 0.1 | ± 5% |
| Silver | — | — | 0.01 | ± 10% |
| None | — | — | — | ± 20% |
Worked Numeric Example
Suppose you pull a molded axial choke from a vintage amplifier and it has the following bands: Yellow, Violet, Brown, Gold.
- Yellow (1st): 4
- Violet (2nd): 7
- Brown (Multiplier): 10
- Gold (Tolerance): ± 5%
Calculation: 47 × 10 = 470 µH (which is 0.47 mH) with a 5% tolerance. According to Electronics Tutorials, this 470 µH value is a standard E12 series increment, confirming our reading is correct.
Military Dot Codes, SMD Variants, and Reading Direction
While the 4-band EIA system covers about 95% of through-hole inductors you will encounter on a workbench, you will occasionally run into legacy military specifications or modern surface-mount alternatives that require a different decoding approach.
The MIL-PRF-15305 Dot System
Older military-spec RF chokes (and some modern equivalents from manufacturers like Vishay/Dale) use painted dots instead of wrap-around bands. The reading sequence is strictly defined by physical placement on the cylindrical body:
- Top Dot (closest to the lead or wide end): Multiplier.
- Middle Two Dots: Significant digits (read top-to-bottom or left-to-right depending on the specific MIL revision, but usually top is 1st digit, bottom is 2nd digit).
- Bottom Dot: Tolerance.
Bench Tip: If the top dot is Silver, the multiplier is 0.01. A Silver-Red-Green-Black dot sequence translates to 25 × 0.01 = 0.25 µH. Always verify the manufacturer datasheet for the exact MIL revision, as some 1970s-era chokes reversed the multiplier and first-digit positions.
SMD Inductor Text Codes (The Modern Variant)
If you are repairing modern switch-mode power supplies (SMPS) or RF boards, you will rarely see color bands. Surface-mount inductors use a 3-digit EIA text code printed directly on the ferrite or iron core, functioning exactly like SMD resistor codes but yielding µH.
- Code '101': 10 × 10¹ = 100 µH
- Code '4R7': The 'R' acts as a decimal point = 4.7 µH
- Code 'N47': The 'N' acts as a decimal for nano/low-micro = 0.47 µH (470 nH)
Solving the 'Read Direction' Problem
Unlike resistors, which often have a distinct gold/silver tolerance band on the right, inductors frequently use colors for tolerance that can also be digits (like Brown or Red). To determine the correct reading direction:
- Look for a band that is physically thicker than the others; this is the first digit.
- Look at the spacing. The first band is usually positioned closer to the axial lead wire than the tolerance band is to the opposite lead.
- If the component has a silver or gold band, that is almost certainly the tolerance band and belongs on the far right.
The 'Rows People Get Wrong' and Testing Faded Components
Even experienced technicians make specific errors when translating inductor color codes. Furthermore, heat, flux residue, and age frequently destroy these markings, requiring instrumental verification.
The most common mistake is assuming the final calculated number is in milliHenries (mH) or Henries (H). The EIA inductor color code always defaults to microHenries (µH). A reading of 'Brown-Black-Orange' is 10,000 µH (which equals 10 mH), not 10,000 mH. Always do the mental conversion to verify the value makes physical sense for the component's size.
Common Misinterpretations
- Gold and Silver as Multipliers: People forget that Gold and Silver can be in the 3rd position. Gold in the multiplier position means × 0.1, and Silver means × 0.01. A Brown-Black-Gold-Gold inductor is 10 × 0.1 = 1.0 µH at 5% tolerance.
- Missing Tolerance Band: If an inductor only has three bands, the tolerance defaults to ± 20%. This is incredibly common on cheap, unbranded power chokes used in low-cost LED drivers.
- Confusing Core Color Codes with Inductance Codes: Toroidal inductors (like Micrometals iron powder cores) use color codes to indicate the core material mix (e.g., Yellow/White is Mix -26), not the inductance. The inductance of a toroid depends entirely on the number of wire turns wrapped around it, which cannot be read via a color code.
Safe Interpretation When Markings are Faded or Missing
When paint chips off or a component is scorched, do not guess the value based on circuit position alone. You must measure it with an LCR meter. However, measuring inductors is highly frequency-dependent due to core permeability roll-off and parasitic capacitance, a phenomenon detailed in Analog Devices' technical literature on Self-Resonant Frequency (SRF).
The LCR Meter Testing Framework:
- For Molded RF Chokes (Color-banded axial types): Set your LCR meter (e.g., DER EE DE-5000 or Keysight U1733C) to 100 kHz or higher. These use ferrite cores designed for high frequencies. If you test them at the default 100 Hz or 1 kHz used for power transformers, the meter will often display an error or a wildly inflated value due to the test signal being too far below the core's operational permeability curve.
- For Power Chokes (Iron core, thick wire, SMD shielded types): Set the LCR meter to 100 Hz or 1 kHz. These are used in buck/boost converters and audio crossovers. Testing them at 100 kHz may push the measurement past their SRF, resulting in a capacitive reading (negative inductance) on your meter.
- Verify DCR: After measuring inductance (L), switch the meter to measure DC Resistance (DCR). A healthy color-coded RF choke should have a DCR between 0.5 Ω and 15 Ω. If the DCR is infinite, the internal wire bond has snapped, regardless of what the color bands say.
By combining the EIA chart above with proper LCR meter frequency selection, you can accurately identify, replace, and verify any inductor on the bench, ensuring your filters, oscillators, and power supplies operate exactly as designed.
