Resistor Color Codes: The Secret Language

5,800 searches/month for "resistor color codes" — because without this knowledge, you can't repair electronics, build circuits, or identify why a component failed.

Resistors don't have numbers printed on them (too small). Instead, they use colored bands to encode resistance value, tolerance, and sometimes temperature coefficient:

• Brown-Black-Red-Gold: 1,000Ω (1kΩ) ±5%
• Red-Red-Brown-Gold: 220Ω ±5%
• Yellow-Violet-Orange-Gold: 47,000Ω (47kΩ) ±5%

This color code system has been standard since the 1920s. Every technician, engineer, and electronics hobbyist must memorize it. There's no alternative — you can't work on circuit boards without reading resistors.

---

The Core System: How Color Codes Work

The Standard 4-Band Code (Most Common)

Resistors have 4 colored bands read from left to right (start at the end with bands closer together, or where gold/silver tolerance band is on the right).

Band 1: First digit (0-9) Band 2: Second digit (0-9) Band 3: Multiplier (10⁰ to 10⁹) Band 4: Tolerance (accuracy)

The Color-to-Number Table

Memory Aids (Mnemonics)

Most popular (PG-rated):

Big Brown Rabbits Often Yield Great Big Vegetable Gardens Weekly

Engineering classic:

Better Be Right Or Your Great Big Venture Goes Wrong

Professional standard:

Black = 0, Brown = 1, Red = 2, Orange = 3, Yellow = 4, Green = 5, Blue = 6, Violet = 7, Gray = 8, White = 9

---

Quick Reference: Common Resistor Values

E12 series (±10%): 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 E24 series (±5%): All E12 values + intermediate values

---

Real-World Application 1: Reading a 4-Band Resistor

Example: Brown-Black-Red-Gold

Step 1: Identify orientation

• Gold band on right = tolerance band
• Start reading from left

Step 2: Decode bands

• Band 1 (Brown): Digit 1
• Band 2 (Black): Digit 0
• Band 3 (Red): Multiplier ×10² (×100)
• Band 4 (Gold): Tolerance ±5%

Step 3: Calculate resistance

Resistance = (Digit1)(Digit2) × Multiplier
Resistance = 10 × 100 = 1,000Ω = 1kΩ

Step 4: Apply tolerance

Min: 1,000Ω - 5% = 950Ω
Max: 1,000Ω + 5% = 1,050Ω

Result: 1kΩ ±5% (actual value between 950-1,050Ω)

---

Example: Yellow-Violet-Orange-Gold

Band 1 (Yellow): 4 Band 2 (Violet): 7 Band 3 (Orange): ×10³ (×1,000) Band 4 (Gold): ±5%

Calculation:

47 × 1,000 = 47,000Ω = 47kΩ ±5%
Min: 44.65kΩ, Max: 49.35kΩ

---

Example: Red-Red-Green-Gold

Band 1 (Red): 2 Band 2 (Red): 2 Band 3 (Green): ×10⁵ (×100,000) Band 4 (Gold): ±5%

Calculation:

22 × 100,000 = 2,200,000Ω = 2.2MΩ ±5%

---

Real-World Application 2: The 5-Band Code (Precision Resistors)

Precision resistors (±1% or better) use 5 bands for an extra digit of accuracy.

Band 1: First digit Band 2: Second digit Band 3: Third digit Band 4: Multiplier Band 5: Tolerance

Example: Brown-Red-Green-Brown-Brown

Band 1 (Brown): 1 Band 2 (Red): 2 Band 3 (Green): 5 Band 4 (Brown): ×10¹ (×10) Band 5 (Brown): ±1%

Calculation:

125 × 10 = 1,250Ω = 1.25kΩ ±1%
Min: 1,237.5Ω, Max: 1,262.5Ω

Why 5 bands? Standard 4-band can only represent 10-99 × multiplier. 5-band adds precision: 100-999 × multiplier.

Use cases:

• Medical devices: Blood pressure monitors (0.1% tolerance)
• Precision audio: Studio equipment (0.5% tolerance)
• Measurement equipment: Voltmeters, ohmmeters (0.1% or better)

---

Real-World Application 3: Troubleshooting Failed Circuits

Burned Resistors: Reading Damaged Color Codes

The problem: Resistor overheated, bands are charred/discolored.

Diagnostic approach:

1. Check adjacent resistors:

• Same value resistors often used in pairs (voltage dividers, differential pairs)
• Symmetric circuit sections use identical values

2. Measure with multimeter (if partially intact):

• Set to Ω mode
• Out-of-circuit reading (desoldered) is accurate
• In-circuit reading may be affected by parallel paths

3. Reverse-engineer from circuit function:

Example: LED current-limiting resistor (burned out)

Known values:

• Supply voltage: 5V
• LED forward voltage: 2V (red LED typical)
• Desired current: 20 mA

Calculate original resistor:

R = (V_supply - V_LED) / I
R = (5V - 2V) / 0.02A = 150Ω

Closest standard value: 150Ω (Brown-Green-Brown-Gold)

Why it burned: Likely 1/8W resistor used instead of 1/4W.

Power dissipation:

P = I² × R = 0.02² × 150 = 0.06W

1/8W resistor (0.125W): Marginal (operating at 48% capacity) 1/4W resistor (0.25W): Safe (operating at 24% capacity)

Design rule: Use resistor rated ≥2× calculated power dissipation.

---

Real-World Application 4: LED Current Limiting (Why Resistor Value Matters)

Problem: LED too dim or too bright

Scenario: Circuit uses Red-Red-Brown-Gold (220Ω) for LED. Light output is wrong.

Step 1: Verify LED specs

• Forward voltage (V_f): 2.0V (red), 3.2V (white/blue), 1.8V (IR)
• Optimal current: 20 mA (most 5mm LEDs)

Step 2: Calculate actual current

For red LED (V_f = 2.0V) with 220Ω:

I = (V_supply - V_LED) / R
I = (5V - 2.0V) / 220Ω = 0.0136A = 13.6 mA

Result: 13.6 mA < 20 mA → LED dimmer than optimal.

For white LED (V_f = 3.2V) with 220Ω:

I = (5V - 3.2V) / 220Ω = 0.0082A = 8.2 mA

Result: 8.2 mA << 20 mA → LED very dim.

Choosing Correct Resistor

Target: 20 mA for both LED types

Red LED:

R = (5V - 2.0V) / 0.02A = 150Ω
Closest standard: 150Ω (Brown-Green-Brown)

White LED:

R = (5V - 3.2V) / 0.02A = 90Ω
Closest standard: 100Ω (Brown-Black-Brown)

Why different resistors? LED forward voltage varies by color. Always calculate per LED type.

---

The 6-Band Code (Temperature Coefficient)

For ultra-precision applications (< 0.1% tolerance), a 6th band specifies how resistance changes with temperature.

Band 6 colors:

• Brown: 100 ppm/°C
• Red: 50 ppm/°C
• Orange: 15 ppm/°C
• Yellow: 25 ppm/°C
• Blue: 10 ppm/°C
• Violet: 5 ppm/°C

ppm (parts per million): How many Ω change per 1 million Ω per °C.

Example: 10kΩ resistor with 100 ppm/°C

Temperature change: 25°C → 75°C (50°C increase)

Resistance change:

ΔR = R × ppm × ΔT / 1,000,000
ΔR = 10,000Ω × 100 × 50 / 1,000,000 = 50Ω

New resistance: 10,000Ω + 50Ω = 10,050Ω (0.5% change)

Why this matters:

• Precision instrumentation: Temperature drift causes measurement error
• Audio equipment: Tone shift with amplifier heating
• Reference circuits: Voltage regulators require stable resistors

Applications requiring low temp coefficient:

• Medical devices (body temp variation)
• Outdoor sensors (-40°C to +85°C range)
• Aerospace (extreme thermal cycling)

---

Common Mistakes When Reading Resistors

Mistake 1: Reading from wrong end

Incorrect: Gold-Red-Black-Brown (backward) Correct: Brown-Black-Red-Gold (1kΩ)

How to avoid:

• Gold/silver tolerance band always on right
• Bands grouped closer to left starting point

Mistake 2: Confusing orange and red

In poor lighting:

• Red appears dark orange
• Orange appears bright red

Solution: Use multimeter to verify, or compare to known resistor.

Mistake 3: Misreading violet as gray

Violet (7) vs. Gray (8) — easily confused.

Impact:

• Yellow-Violet-Orange = 47kΩ
• Yellow-Gray-Orange = 48kΩ
• 2% difference (may or may not matter)

Mistake 4: Ignoring tolerance

220Ω ±5%: 209-231Ω actual range 220Ω ±1%: 217.8-222.2Ω actual range

When tolerance matters:

• Precision filters (audio crossovers)
• Timing circuits (555 timer frequency)
• Reference circuits (voltage dividers for ADCs)

When tolerance doesn't matter:

• LED current limiting (human eye can't detect 5% brightness change)
• Pull-up resistors (anywhere 1k-10k works)

---

SMD Resistors: The Numerical Code

Surface-mount devices (SMD) use numerical codes instead of color bands (too small for stripes).

3-Digit Code (Standard)

Format: AB(C)

• A, B: Significant digits
• C: Multiplier (number of zeros)

Examples:

• 103: 10 × 10³ = 10,000Ω = 10kΩ
• 472: 47 × 10² = 4,700Ω = 4.7kΩ
• 220: 22 × 10⁰ = 22Ω

4-Digit Code (Precision)

Format: ABC(D)

• A, B, C: Significant digits
• D: Multiplier

Examples:

• 1001: 100 × 10¹ = 1,000Ω = 1kΩ
• 4702: 470 × 10² = 47,000Ω = 47kΩ

Special Codes

R indicates decimal point:

• 5R6: 5.6Ω
• R220: 0.22Ω

Why SMD uses numbers: Printing color bands on 0.5mm × 0.25mm resistors is impossible.

---

Practical Example: Repairing a Circuit Board

Problem: Arduino project not working — one resistor burned

Circuit: Push button with pull-down resistor

Burned resistor location: Between GPIO pin and ground

Step 1: Identify resistor value from schematic (if available)

• Schematic shows 10kΩ pull-down

Step 2: If no schematic, reverse-engineer

• Pull-down resistors typically 10kΩ (standard practice)
• Alternatives: 1kΩ (strong pull-down) or 47kΩ (weak pull-down)

Step 3: Decode adjacent resistors (if visible)

• Neighboring resistor: Brown-Black-Orange-Gold = 10kΩ
• Likely burned resistor was also 10kΩ

Step 4: Measure with multimeter (if partially intact)

• Reading: 12.3kΩ (damaged, but close to 10kΩ)
• Confirms 10kΩ ±5% original value

Step 5: Replace with correct resistor

• Color code: Brown-Black-Orange-Gold (10kΩ ±5%)
• Power rating: 1/4W (overkill for digital circuits, but safe)

Step 6: Verify why it burned

• GPIO pin shorted to ground? (would pull full 5V across 10kΩ = 2.5 mA, harmless)
• Likely cause: Overcurrent from faulty IC or short elsewhere

Result: Replacing resistor fixes immediate problem, but investigate root cause to prevent reoccurrence.

---

How Calculators Make This Easier

Manual resistor decoding requires:

1. Memorizing color-to-number table
2. Calculating multiplier (10^n)
3. Unit conversion (Ω → kΩ → MΩ)
4. Tolerance range calculation (±%)

Modern calculators provide:

• Color band selector (dropdown menus)
• Instant resistance value
• Tolerance range display
• Reverse lookup (enter resistance, get color bands)

Example scenario: You need a 4.7kΩ resistor. What colors should you look for?

Calculator input: 4,700Ω

Calculator output:

• 4-band: Yellow-Violet-Red-Gold (4, 7, ×100, ±5%)
• 5-band: Yellow-Violet-Black-Brown-Brown (4, 7, 0, ×10, ±1%)
• SMD code: 472

Manual lookup in charts: 30+ seconds. Calculator: instant.

Professional use: Technicians use resistor calculators for:

• Quick identification during repair
• Bill of materials (BOM) generation
• Verifying schematic values match physical components
• Training new technicians (visual reference)

These tools aren't shortcuts — they're standard practice. Even experienced engineers use calculators to avoid errors when working with unfamiliar color codes (6-band temp coefficient resistors, etc.).

---

Summary: Why Everyone Must Know Resistor Codes

The system: Color bands encode resistance (2-3 digits + multiplier) and tolerance. Standard since 1920s, universal across all electronics.

Key insights:

1. 4-band code (most common): digit-digit-multiplier-tolerance
2. 5-band code (precision): digit-digit-digit-multiplier-tolerance
3. 6-band code (ultra-precision): adds temperature coefficient
4. SMD numerical code: 3-4 digits (no color bands)

Common values to memorize:

• 220Ω (Red-Red-Brown): LED limiting
• 1kΩ (Brown-Black-Red): Pull-up/pull-down
• 10kΩ (Brown-Black-Orange): Most common — general purpose
• 47kΩ (Yellow-Violet-Orange): Audio circuits

Real-world necessity:

• Cannot repair circuit boards without reading resistors
• Cannot substitute components without knowing values
• Cannot design circuits without specifying standard values
• Cannot troubleshoot failures without verifying resistances

The bottom line: Resistor color codes are the minimum knowledge requirement for electronics work. Every technician certification exam tests this. Every repair job requires it. Every circuit design relies on it.

Whether you're fixing a guitar amplifier, troubleshooting an Arduino project, or reverse-engineering vintage electronics, you cannot proceed without decoding these colored bands.

Learn the mnemonic. Memorize the table. Verify with a multimeter. This isn't optional — it's the secret language of electronics.