Most engineers learn 4-band resistor color codes in school and never think about it again. Then one day you're designing a precision analog circuit, you crack open a parts bin, and there's a resistor with six colored bands staring back at you. The first four bands make sense. The fifth is the tolerance. But the sixth?
That sixth band is the temperature coefficient — also called the TCR (Temperature Coefficient of Resistance). And for precision circuits, it matters a lot.
Quick Recap: 4-Band and 5-Band Codes
Before we tackle 6-band resistors, let's make sure we're on the same page.
4-band resistors are the standard through-hole parts you see everywhere:
- Band 1: First significant digit
- Band 2: Second significant digit
- Band 3: Multiplier (power of 10)
- Band 4: Tolerance
Example: Brown-Black-Red-Gold = 1-0-×100-±5% = 1kΩ ±5%
5-band resistors add a third significant digit for tighter values:
- Band 1: First significant digit
- Band 2: Second significant digit
- Band 3: Third significant digit
- Band 4: Multiplier
- Band 5: Tolerance
Example: Brown-Black-Black-Brown-Brown = 1-0-0-×10-±1% = 1kΩ ±1%
The 6-Band Resistor
A 6-band resistor adds one more band after tolerance:
- Band 1: First significant digit
- Band 2: Second significant digit
- Band 3: Third significant digit
- Band 4: Multiplier
- Band 5: Tolerance
- Band 6: Temperature coefficient (ppm/°C)
The temperature coefficient tells you how much the resistance changes per degree Celsius, expressed in parts per million.
Temperature Coefficient Color Chart
| Color | TCR (ppm/°C) |
|---|---|
| Brown | 100 |
| Red | 50 |
| Orange | 15 |
| Yellow | 25 |
| Blue | 10 |
| Violet | 5 |
| White | 1 |
The most common values you'll see in practice are Brown (100 ppm/°C) and Red (50 ppm/°C) on general-purpose precision resistors, and Blue (10 ppm/°C) through Violet (5 ppm/°C) on high-precision parts.
Reading a 6-Band Resistor: Worked Examples
Example 1: Precision 4.7kΩ Resistor
Bands: Yellow - Violet - Black - Brown - Brown - Red
| Band | Color | Meaning |
|---|---|---|
| 1 | Yellow | 4 |
| 2 | Violet | 7 |
| 3 | Black | 0 |
| 4 | Brown | ×10 |
| 5 | Brown | ±1% |
| 6 | Red | 50 ppm/°C |
Value: 470 × 10 = 4,700Ω (4.7kΩ) ±1%, 50 ppm/°C
Example 2: High-Precision 10kΩ Resistor
Bands: Brown - Black - Black - Red - Brown - Violet
| Band | Color | Meaning |
|---|---|---|
| 1 | Brown | 1 |
| 2 | Black | 0 |
| 3 | Black | 0 |
| 4 | Red | ×100 |
| 5 | Brown | ±1% |
| 6 | Violet | 5 ppm/°C |
Value: 100 × 100 = 10,000Ω (10kΩ) ±1%, 5 ppm/°C
This is a high-precision part — 5 ppm/°C means the resistance barely changes with temperature. You'd find this in measurement equipment, calibration references, or medical devices.
Example 3: 100Ω Current Sense Resistor
Bands: Brown - Black - Black - Black - Brown - Blue
| Band | Color | Meaning |
|---|---|---|
| 1 | Brown | 1 |
| 2 | Black | 0 |
| 3 | Black | 0 |
| 4 | Black | ×1 |
| 5 | Brown | ±1% |
| 6 | Blue | 10 ppm/°C |
Value: 100 × 1 = 100Ω ±1%, 10 ppm/°C
What Does ppm/°C Actually Mean?
Parts per million per degree Celsius. Let's make this concrete.
A resistor with 50 ppm/°C means that for every 1°C change in temperature, the resistance changes by 50 parts per million, or 0.005%.
Calculation:
ΔR = R × TCR × ΔT / 1,000,000
For our 4.7kΩ, 50 ppm/°C resistor experiencing a 40°C temperature rise (from 25°C to 65°C):
ΔR = 4700 × 50 × 40 / 1,000,000
ΔR = 9.4Ω
So the resistance shifts from 4,700Ω to 4,709.4Ω. That's a 0.2% change. If this resistor is in a voltage divider setting a reference voltage, your reference just drifted 0.2%.
Is that a problem? Depends on the application:
| Application | Acceptable Drift | Typical TCR Needed |
|---|---|---|
| Pull-up/pull-down | Don't care | 100+ ppm/°C is fine |
| LED current limiting | < 5% | 100 ppm/°C is fine |
| Op-amp feedback | < 0.5% | 50 ppm/°C or better |
| Voltage reference divider | < 0.1% | 10-25 ppm/°C |
| Current sensing | < 0.05% | 5 ppm/°C or better |
| Calibration standard | < 0.01% | 1-5 ppm/°C |
Comparison: How Much Does TCR Really Matter?
Let's compare three 10kΩ resistors over a 50°C temperature swing:
| TCR | Resistance at 25°C | Resistance at 75°C | Change | % Change |
|---|---|---|---|---|
| 100 ppm/°C | 10,000Ω | 10,050Ω | +50Ω | +0.50% |
| 50 ppm/°C | 10,000Ω | 10,025Ω | +25Ω | +0.25% |
| 10 ppm/°C | 10,000Ω | 10,005Ω | +5Ω | +0.05% |
| 5 ppm/°C | 10,000Ω | 10,002.5Ω | +2.5Ω | +0.025% |
In a voltage divider with two 10kΩ resistors (50 ppm/°C) across a 5V reference, a 50°C temperature rise shifts the midpoint by about 6mV. For a 12-bit ADC with a 5V range (1.22mV per LSB), that's a 5 LSB drift. Not catastrophic, but noticeable.
For a 16-bit ADC, that same 6mV drift is 79 LSB. Your measurement just got noisy.
Which Way Do You Read It?
6-band resistors can be confusing because there's sometimes a gap before the tolerance band, and sometimes there isn't. Here's how to orient the resistor correctly:
-
Look for the gap. There's usually a wider gap between the multiplier band and the tolerance band. Hold the resistor so the wider gap is on the right.
-
Tolerance band is typically gold or silver. If one end has a gold or silver band, that's the tolerance (rightmost of the value bands). The TCR band will be to its right.
-
The TCR band is never gold or silver. It's always a spectral color (brown through white). This helps distinguish it from the multiplier.
-
When in doubt, measure it. A multimeter takes 5 seconds and eliminates all ambiguity.
When Do You Actually Need 6-Band Resistors?
You don't need them for most designs. Here's when they show up:
You need 6-band resistors when:
- Designing precision measurement circuits (ADC front-ends, sensor signal conditioning)
- Building current sense circuits where drift directly affects accuracy
- Creating voltage references or calibration circuits
- Working in environments with wide temperature swings (automotive: -40°C to +125°C)
- Your circuit's error budget analysis shows resistor drift is a significant contributor
You don't need them for:
- General-purpose digital pull-ups and pull-downs
- LED current limiting
- RC filter networks in non-critical paths
- Power supply bulk decoupling
- Anything where ±5% tolerance is acceptable
Practical Tips
SMD resistors are easier. If you're designing new boards, just use surface-mount resistors. They're marked with numeric codes (4702 = 47kΩ, 1002 = 10kΩ) and the TCR is specified in the datasheet, not printed on the part. No color code confusion.
Match TCR in critical pairs. If you're building a differential amplifier or instrumentation amp, the ratio between resistors matters more than absolute value. Using resistors from the same batch (same TCR) means they drift together, keeping the ratio stable.
Datasheet over color code. Always. The color code tells you the nominal value, but the datasheet tells you the actual tolerance, TCR curve (it's not perfectly linear), and stability over time. Resistor aging (long-term drift) can be as significant as temperature drift in precision applications. Check the "Load Life" spec — typically 0.5-1% drift per 1000 hours at rated power.
Self-heating is sneaky. When current flows through a resistor, it dissipates power (P = I²R). That power heats the resistor, which changes its resistance. A 10kΩ, 50 ppm/°C resistor dissipating 0.1W might self-heat by 20-30°C above ambient, causing an additional 0.1-0.15% drift. Derate your resistors and check the datasheet's thermal resistance (usually expressed in °C/W).
6-Band Resistor Quick Reference Card
| Band Position | 4-Band | 5-Band | 6-Band |
|---|---|---|---|
| Band 1 | 1st digit | 1st digit | 1st digit |
| Band 2 | 2nd digit | 2nd digit | 2nd digit |
| Band 3 | Multiplier | 3rd digit | 3rd digit |
| Band 4 | Tolerance | Multiplier | Multiplier |
| Band 5 | — | Tolerance | Tolerance |
| Band 6 | — | — | TCR (ppm/°C) |
| Digit | Color | Multiplier |
|---|---|---|
| 0 | Black | ×1 |
| 1 | Brown | ×10 |
| 2 | Red | ×100 |
| 3 | Orange | ×1k |
| 4 | Yellow | ×10k |
| 5 | Green | ×100k |
| 6 | Blue | ×1M |
| 7 | Violet | ×10M |
| 8 | Gray | ×100M |
| 9 | White | ×1G |
| Tolerance | Color |
|---|---|
| ±1% | Brown |
| ±2% | Red |
| ±0.5% | Green |
| ±0.25% | Blue |
| ±0.1% | Violet |
| ±5% | Gold |
| ±10% | Silver |
Want to double-check your reading? Use the Resistor Color Code Calculator — select the number of bands, click the colors, and it gives you the value, tolerance, and temperature coefficient instantly. Supports 4, 5, and 6-band resistors.