The 4-band 100 ohm color code is Brown, Black, Brown, Gold. The 5-band precision equivalent is Brown, Black, Black, Black, Gold (or Brown for 1% tolerance). If you are holding a through-hole resistor and need to verify its value before soldering it into a current-limiting or pull-up circuit, use the reference table below.
The 100 Ohm Color Code Reference Table
Resistor color codes follow a strict digit-digit-multiplier-tolerance sequence. The table below maps the exact band colors for the most common 100Ω through-hole formats, alongside their surface-mount (SMD) equivalents.
| Format | Band 1 (Digit) | Band 2 (Digit) | Band 3 (Digit/Mult) | Band 4 (Mult/Tol) | Band 5 (Tol) | SMD Code |
|---|---|---|---|---|---|---|
| 4-Band (±5%) | Brown (1) | Black (0) | Brown (×10) | Gold (±5%) | - | 101 |
| 5-Band (±1%) | Brown (1) | Black (0) | Black (0) | Black (×1) | Brown (±1%) | 1000 |
| 5-Band (±2%) | Brown (1) | Black (0) | Black (0) | Black (×1) | Red (±2%) | 1000 |
| 6-Band (±1%, 100ppm) | Brown (1) | Black (0) | Black (0) | Black (×1) | Brown (±1%) | - |
Standard Variants: IEC 60062 vs. Regional Wire Codes
A frequent point of confusion on the workbench is conflating resistor band standards with wire insulation standards. The 100 ohm resistor color code is universally governed by IEC 60062. There is no 'US vs UK' resistor color code; a Brown-Black-Brown-Gold resistor means 100Ω in Tokyo, Berlin, and Chicago alike.
However, if you are stripping a 100-ohm impedance cable (such as RS-485, DMX512, or AES/EBU audio twisted pair) and looking at the wire colors inside the jacket, regional wiring standards apply. This is where beginners make dangerous or signal-destroying assumptions:
| Standard / Region | Line / Hot / Data+ | Neutral / Return / Data- | Ground / Shield |
|---|---|---|---|
| NEC (US / Canada) | Black | White | Green or Bare |
| IEC 60446 (EU / Modern UK) | Brown | Blue | Green/Yellow Stripe |
| Old UK (Pre-2004) | Red | Black | Green |
Rows People Get Wrong & Faded Band Recovery
Even experienced technicians misread 100Ω resistors under specific conditions. Here are the most common failure modes and how to resolve them.
1. The Warm LED Color Shift (Brown vs. Red)
Under 2700K to 3000K warm-white workbench LEDs, the red pigment in a 120Ω resistor (Brown-Red-Brown) and the brown pigment in a 100Ω resistor look nearly identical. The Fix: Move the component under a 5000K daylight lamp or take it to a window with natural sunlight. If you are designing a lab, install 5000K CRI>90 lighting at your main soldering station to eliminate this exact error.
2. The 5-Band Multiplier Trap
Readers accustomed to 4-band resistors often read a 5-band 100Ω resistor (Brown-Black-Black-Black-Brown) as a 4-band, ignoring the third digit. They see Brown(1)-Black(0)-Black(×1) and calculate 10Ω, or they misread the multiplier and calculate 10kΩ. The Fix: Count the bands first. If there are five, the fourth band is always the multiplier. For 100Ω, that multiplier is Black (×1).
3. Faded Carbon Film Bands
Vintage carbon film resistors (especially from 1970s-1980s consumer electronics) suffer from UV and heat degradation. Brown fades to a muddy orange; black fades to a dark, bruised green. Safe Interpretation: Do not guess. Place the resistor on a breadboard, set your digital multimeter to the 200Ω range, and measure across the leads.
- Expected 100Ω (±5% Gold): Reads between 95.0Ω and 105.0Ω.
- Expected 100Ω (±1% Brown): Reads between 99.0Ω and 101.0Ω.
- If it reads ~115Ω: It is actually a 120Ω resistor (Brown-Red-Brown).
- If it reads >120Ω or open (OL): The resistor has failed open due to thermal overstress. Discard it.
Decision Path: Which 100Ω Resistor to Buy
Not all 100Ω resistors are created equal. The color code tells you the nominal value, but the physical construction dictates how it behaves under load, heat, and high-frequency signals. Use this decision tree to select the exact part number for your bill of materials (BOM).
| If your application is... | Then choose this technology... | Concrete Part Pick (DigiKey/Mouser) |
|---|---|---|
| General purpose, LED current limiting, breadboard prototyping, pull-ups. | 1/4W Carbon Film (5% tolerance, cheap, high noise). | Yageo CFR-25JB-52-100R |
| Precision analog, audio crossovers, DAC output stages, low-noise requirements. | 0.6W Metal Film (1% tolerance, low thermal noise, stable). | Vishay MRS25000C1000FRP00 |
| Current shunt measurement, high-surge inrush limiting, motor snubbers. | 1W to 3W Wirewound or Metal Oxide (high pulse survival). | Vishay PR03000201000JAC00 (3W Metal Glaze) |
| High-density SMD PCB layout, automated pick-and-place assembly. | 0805 Thick Film (1% tolerance, 1/8W, compact). | Bourns CR0805-FX-1000ELF |
SMD Equivalents and High-Power Bench Notes
When transitioning from through-hole to surface-mount devices (SMD), the color bands disappear, replaced by alphanumeric silkscreen codes. Understanding these is critical for rework and debugging modern PCBs.
Decoding SMD 100Ω Resistors
- 3-Digit Code (Standard 5%):
101. The first two digits are the significant figures (10), and the third is the multiplier (10^1). 10 × 10 = 100Ω. - 4-Digit Code (Precision 1%):
1000. The first three digits are significant (100), and the fourth is the multiplier (10^0). 100 × 1 = 100Ω. - EIA-96 Code (High Precision):
01A. The '01' corresponds to the value 100 in the EIA-96 lookup table, and 'A' is the multiplier for ×1.
For high-power applications (such as dummy loads or power supply bleeder networks), a single 100Ω resistor will quickly exceed its thermal limits. If you need to dissipate 5W across a 100Ω load, do not buy a single 5W wirewound resistor unless you have adequate heatsinking and airflow. Instead, wire five 1/4W 500Ω resistors in parallel, or five 1W 20Ω resistors in series. This distributes the thermal mass across a wider PCB area, preventing localized hot spots that can delaminate FR4 fiberglass or scorch the solder mask. For a comprehensive look at resistor derating curves and thermal management, refer to the All About Circuits resistor reference guide and always consult the specific manufacturer's datasheet for ambient temperature derating charts.
