120 Ohm Resistor Color Code — RS-485 Termination & Bright LED
120 Ω color code (Brown-Red-Brown-Gold): CAN/RS-485 bus termination at 120 Ω, brighter 5 V LED current vs 220 Ω, and the 12 Ω black-multiplier trap.
Decode band colors instantly
Full index: All resistor color code values
120 Ω: bus termination and brighter LEDs
Brown · Red · Brown · Gold → digits 1 · 2, multiplier ×10 → 120 Ω. This page covers RS-485/CAN termination and higher LED current on 5 V — not RC timing (100 Ω guide) or the standard maker default (220 Ω guide).
4-band: Brown · Red · Brown · Gold → 12 × 10 = 120 Ω (±5%) · 5-band (±1%): Brown · Red · Black · Black · Brown → 120 × 1 = 120 Ω (±1%)
Tolerance window (±5%): 114 Ω – 126 Ω · Method: beginner's guide · Tool: calculator
RS-485 / CAN: why 120 Ω is the magic number
Many differential field buses specify 120 Ω characteristic impedance — terminate the line ends with 120 Ω between the differential pair (implementation varies by transceiver — always follow your datasheet):
| Bus type | Termination | Color code on the part |
|---|---|---|
| RS-485 (typical) | 120 Ω at each end of long runs | Brown · Red · Brown · Gold |
| CAN (high speed) | 120 Ω across CAN_H / CAN_L | Same bands |
Wrong value causes reflections and framing errors — color code identifies the part value, not whether your topology needs termination (short bench links often omit it).
LED on 5 V: 120 Ω vs 220 Ω vs 330 Ω
| Series R | Current ($V_f ≈ 2 V$) | Brightness | Resistor power |
|---|---|---|---|
| 120 Ω | ~25 mA | Very bright — check LED max $I_F$ | ≈ 75 mW |
| 220 Ω | ~13 mA | Kit default | ≈ 45 mW |
| 330 Ω | ~9 mA | Moderate | ≈ 30 mW |
$I = (5 − V_f) / R$. At 25 mA many 3 mm indicator LEDs are near their rating — use 220 Ω for safer headroom or our LED calculator.
Confusing 120 Ω with 12 Ω
| Value | Bands (4-band) | Multiplier |
|---|---|---|
| 120 Ω | Brown · Red · Brown | ×10 |
| 12 Ω | Brown · Red · Black | ×1 |
If the meter reads ~12 Ω but you expected 120 Ω, re-check band order — tolerance band on the right.
Power check before soldering
| Load | Calculation | 1/4 W OK? |
|---|---|---|
| 5 V LED @ 120 Ω | $P = (5−2) × 0.025 ≈ 75 mW$ | Yes |
| 12 V into 120 Ω (dummy load) | $P = 144/120 = 1.2 W$ | No — needs ≥2 W part |
Color code does not indicate wattage — body size does.
FAQ
What is the 120 ohm resistor color code?
4-band (±5%): Brown, Red, Brown, Gold. 12 × 10 = 120 Ω (±5%). Actual range: 114 Ω – 126 Ω.
What is the 120 ohm resistor colour code (5-band)?
Brown · Red · Black · Black · Brown → 120 × 1 = 120 Ω (±1%). Range: 118.8 Ω – 121.2 Ω.
How do I read a 120 ohm resistor color code?
Read left to right: first bands are digits, then multiplier, then tolerance. For 120 Ω: Brown-Red-Brown = significant digits & multiplier, Gold = tolerance. Use the color code calculator to verify.
Which end do I start reading a 120 Ω resistor from?
Start from the grouped digit bands (left). The tolerance band (Gold) is on the right — gold and silver are almost always tolerance, not multipliers.
What is the difference between 4-band and 5-band for 120 Ω?
4-band (Brown · Red · Brown · Gold) gives 12 × 10 = 120 Ω (±5%) with typical ±5% gold tolerance. 5-band (Brown · Red · Black · Black · Brown) adds a third digit for ±1% precision: 120 × 1 = 120 Ω (±1%) (118.8 Ω – 121.2 Ω).
120 vs 100 ohm color code?
100 Ω is Brown-Black-Brown. 120 Ω is Brown-Red-Brown — second band differs.
Related guides (different topics)
- 100 Ω color code — RC τ table & wattage at 12 V
- 220 Ω color code — LED brightness vs 330/470 Ω on 5 V
- 470 Ω color code — textbook LED history & Y-V family
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More resistor color code guides
Learn the method in our beginner's guide · Decode instantly with the color code calculator