The resistor color code is an Electronic Industries Alliance (EIA) standard system that uses colored bands to indicate resistance in ohms (Ω), multiplier, and tolerance. For a standard 4-band through-hole resistor, the first two bands represent significant digits, the third is the decimal multiplier, and the fourth indicates the manufacturing tolerance. If you are holding a standard carbon or metal film resistor, orient it so the gold or silver tolerance band is on the far right, and read left to right.
The Complete Resistor Color Code Reference Table
This table covers the universal EIA color standard. It applies to 4-band, 5-band, and 6-band axial resistors. For 5-band resistors (typically 1% metal film), the first three bands are significant digits, the fourth is the multiplier, and the fifth is tolerance. For 6-band resistors, the sixth band indicates the temperature coefficient (ppm/°C).
| Color | Significant Digit (1st/2nd/3rd) | Multiplier (10^x) | Tolerance | Temp Coeff (6th Band) |
|---|---|---|---|---|
| Black | 0 | 1 (10^0) | — | 250 ppm/°C |
| Brown | 1 | 10 (10^1) | ±1% (F) | 100 ppm/°C |
| Red | 2 | 100 (10^2) | ±2% (G) | 50 ppm/°C |
| Orange | 3 | 1k (10^3) | — | 15 ppm/°C |
| Yellow | 4 | 10k (10^4) | — | 25 ppm/°C |
| Green | 5 | 100k (10^5) | ±0.5% (D) | — |
| Blue | 6 | 1M (10^6) | ±0.25% (C) | 10 ppm/°C |
| Violet | 7 | 10M (10^7) | ±0.1% (B) | 5 ppm/°C |
| Gray | 8 | 100M (10^8) | ±0.05% (A) | — |
| White | 9 | 1G (10^9) | — | — |
| Gold | — | 0.1 (10^-1) | ±5% (J) | — |
| Silver | — | 0.01 (10^-2) | ±10% (K) | — |
Regional Standards: EIA Bands vs. IEC 60062 Letter Codes
While the EIA color bands are the global physical standard for through-hole axial resistors, schematic designs and surface-mount devices (SMD) frequently rely on the IEC 60062 standard (historically known as BS1852 in the UK). This system replaces the decimal point with a letter to prevent misreading due to printing errors or magnification issues.
If you are reading a European schematic or ordering SMD equivalents for axial parts, you must translate the color code into IEC letter notation:
- R (Ohms): 4R7 = 4.7Ω (Equivalent to Yellow-Violet-Gold-Gold)
- K (Kilo-ohms): 4K7 = 4,700Ω (Equivalent to Yellow-Violet-Red-Gold)
- M (Mega-ohms): 4M7 = 4,700,000Ω (Equivalent to Yellow-Violet-Green-Gold)
Which standard applies to you? If you are physically holding a through-hole component, use the EIA color table above. If you are reading a PCB silkscreen, a schematic symbol, or coding a BOM for SMD parts, use the IEC 60062 letter codes. Never mix the two on a BOM, as '4K7' and '4700' can cause procurement errors if automated systems strip non-numeric characters.
The Rows People Get Wrong (Common Bench Mistakes)
Even experienced engineers misread resistors under poor lighting or when dealing with non-standard manufacturing batches. Here are the specific rows and scenarios that cause failures, as documented in standard component identification guides.
1. Reading Direction (The Gold/Silver Anchor)
The most common error is reading a 4-band resistor backwards. Rule: Gold and Silver are never used as significant digit bands (the 1st or 2nd band). If you see a gold or silver band on one end, that end is the tolerance band and must be placed on the far right. If a resistor has bands on both ends and neither is gold/silver (common in 5-band 1% resistors), look for a slightly wider gap between the multiplier and tolerance band, or use a multimeter to verify.
2. Gold and Silver as Multipliers vs. Tolerance
People memorize 'Gold = 5%' and forget that Gold can also be a multiplier.
Example: A resistor with bands Brown-Black-Gold-Gold.
Incorrect read: 10Ω ±5%.
Correct read: 1 (Brown) 0 (Black) × 0.1 (Gold multiplier) = 1.0Ω ±5% (Gold tolerance). These 1Ω current-sense resistors are frequently misidentified as 10Ω on the bench.
3. The 'Red Multiplier' Trap in 5-Band Resistors
On a 4-band resistor, Red as a multiplier means ×100. On a 5-band resistor, Red is often the 3rd significant digit (meaning '2'). If you mistake a 5-band 1% resistor for a 4-band 5% resistor, your calculated value will be off by a factor of 10. Always count the physical bands before applying the table.
Decision Tree: Identifying Faded, Burnt, or Missing Resistors
Color bands fade under UV exposure, wash off during aggressive flux cleaning, or burn off entirely during a component failure. When visual identification fails, use this decision path to determine the exact replacement value.
| Condition | Diagnostic Step | Concrete Action / Replacement Pick |
|---|---|---|
| Bands faded but visible under magnification | Use a macro lens or microscope. Look for the underlying ceramic body color (usually beige for carbon, blue for metal film). | If blue body: Assume 1% tolerance (5-band). If beige body: Assume 5% tolerance (4-band). Calculate and order nearest E24 standard value. |
| Bands completely missing / unreadable | Desolder one leg of the resistor to isolate it from the PCB. Measure with a DMM in resistance mode. | If DMM reads within 20% of a standard E12/E24 value, replace with that exact E24 value (e.g., if it reads 4.5kΩ, install a 4.7kΩ). |
| Resistor reads Open (OL) or visibly burnt | The resistor has failed open due to overcurrent. Do not trust the physical bands, as heat alters the carbon composition. | Trace the schematic. If unavailable, identify the node function: GPIO/I2C line = install 10kΩ; LED anode = install 220Ω; Power rail sense = install 0.1Ω. Buy and install that specific value. |
Practical Verification: Measuring and Sizing Tolerances
The color code tells you the nominal value, but the tolerance band dictates the acceptable physical reality. A 1kΩ resistor with a Gold (±5%) band is legally within spec if your multimeter reads anywhere from 950Ω to 1050Ω. When replacing a resistor in a precision circuit (like an op-amp feedback loop or an ADC voltage divider), the color code tolerance is your primary constraint.
- Gold (±5%) / Silver (±10%): Use for pull-ups, pull-downs, LED current limiting, and non-critical biasing. Carbon film composition is typical here.
- Brown (±1%) / Red (±2%): Mandatory for voltage dividers, analog sensor conditioning, and switching power supply feedback networks. Metal film composition is standard.
- Blue (±0.25%) / Violet (±0.1%): Reserved for precision instrumentation, active filters, and medical-grade analog front-ends. These are significantly more expensive and usually ordered in tape-and-reel for automated pick-and-place.
Always verify your replacement resistor with a bench DMM before soldering. A cheap multimeter might have a ±1% baseline error on its own leads. Short the probes, note the lead resistance (usually 0.2Ω to 0.5Ω), and subtract that from your final reading when measuring resistors under 10Ω. Relying solely on the painted bands without bench verification is the fastest way to introduce a 5% gain error into an analog signal chain.
