A 3 band resistor colour code identifies a fixed resistor with a default ±20% tolerance. The first two bands represent significant digits, and the third band is the decimal multiplier. Unlike 4-band or 5-band resistors, there is no tolerance band, meaning the component is generally used in non-critical applications like pull-ups, basic current limiting, or dummy loads where exact precision is not required. If you are holding a component with only three painted rings, you are looking at a 20% tolerance part.
The Complete 3 Band Resistor Colour Code Reference Table
Read the bands starting from the end closest to the wire lead. The table below maps every valid colour to its numeric value and multiplier. Keep this bookmarked for quick bench reference.
| Band Colour | Significant Digit (Bands 1 & 2) | Multiplier (Band 3) | Practical Example (3-Band) |
|---|---|---|---|
| Black | 0 | ×1 (10⁰) | Brown-Black-Black = 10Ω |
| Brown | 1 | ×10 (10¹) | Brown-Brown-Brown = 110Ω |
| Red | 2 | ×100 (10²) | Red-Red-Red = 2.2kΩ |
| Orange | 3 | ×1,000 (10³) | Orange-Orange-Orange = 33kΩ |
| Yellow | 4 | ×10,000 (10⁴) | Yellow-Violet-Orange = 47kΩ |
| Green | 5 | ×100,000 (10⁵) | Green-Blue-Yellow = 560kΩ |
| Blue | 6 | ×1,000,000 (10⁶) | Blue-Grey-Green = 6.8MΩ |
| Violet | 7 | Not typically used | — |
| Grey | 8 | Not typically used | — |
| White | 9 | Not typically used | — |
Note: Gold and Silver are never used in a true 3 band resistor colour code. If you see Gold or Silver, you are actually holding a 4-band or 5-band resistor and miscounting the tolerance or temperature coefficient bands.
Component Standards vs. Regional Wiring Codes (IEC, NEC, UK)
A common point of confusion for beginners crossing over from home electrical work to electronics is assuming that regional wiring colour codes apply to components. They do not. While mains wiring relies on regional standards, resistor colour codes are globally unified under IEC 60062. Your region does not change how you read a resistor.
However, understanding the difference is critical for safety and troubleshooting, especially when salvaging parts from old equipment or working on mixed-signal boards that interface with mains voltage.
| Colour | Resistor Code (IEC 60062 - Global) | Mains Wiring (IEC 60446 - EU/UK/AU) | Mains Wiring (NEC - US/CA) | Old UK Wiring (Pre-2006) |
|---|---|---|---|---|
| Brown | Digit 1 / ×10 | Line (Hot) | Not standard for hot | Line (Hot) |
| Blue | Digit 6 / ×1M | Neutral | Not standard for neutral | Neutral |
| Green | Digit 5 | Not used alone | Equipment Ground | Earth (Ground) |
| Green/Yellow | Not used | Protective Earth (Ground) | Equipment Ground | Not used |
| Black | Digit 0 / ×1 | Line (Hot - switched) | Hot / Neutral (varies) | Neutral |
| Red | Digit 2 / ×100 | Not standard | Hot (240V/Phase 2) | Line (Hot) |
Rows and Scenarios People Get Wrong on the Bench
Even with the chart in front of you, real-world components rarely look like the pristine diagrams in textbooks. Here are the most common pitfalls I see hobbyists and trade students fall into when decoding a 3 band resistor colour code.
1. The 'Black Multiplier' Trap
When the third band is Black, the multiplier is ×1 (10⁰). Many beginners see Black and instinctively think 'zero', assuming the resistor is 0Ω (a jumper). A Brown-Black-Black resistor is not 10Ω with zero multiplier; it is exactly 10Ω. If you need a 0Ω jumper, it will typically be a single black band in the center of the component, not a 3-band code.
2. Heat-Faded Red vs. Orange
Carbon and thick-film resistors subjected to years of heat on a PCB will experience epoxy discolouration. Red bands frequently fade to a burnt orange or brownish hue. I have seen countless hobbyists misread a 220Ω (Red-Red-Brown) as 330Ω (Orange-Orange-Brown) because the resistor was baked near a voltage regulator for a decade.
3. Reading Direction Without a Tolerance Band
On a 4-band resistor, the Gold or Silver tolerance band is spaced slightly further apart, giving you a clear 'start' and 'end'. A true 3 band resistor colour code lacks this spacing cue. To read it correctly, start from the band that is physically closest to the wire lead. If the bands are perfectly centered, look for the manufacturer's logo or text stamping on the component body; the bands are read left-to-right when the text is upright.
Frequently Asked Questions
How do I read a 3 band resistor colour code if the paint is faded?
If visual identification is compromised by UV exposure, heat, or chemical flux residue, abandon the colour code entirely. Desolder one leg of the component to isolate it from the circuit, then measure it directly with a digital multimeter. Cross-reference your measured value against the E24 standard value series (e.g., 1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1) to determine the original intended value.
Why does a 3 band resistor colour code have no tolerance band?
The absence of a fourth band is the indicator itself. According to All About Circuits and standard component manufacturing practices, a missing tolerance band defaults to ±20%. These resistors are cheaper to produce because the factory does not need to sort them into tighter tolerance bins (like 5% or 1%). They are perfectly fine for basic LED current limiting or pull-down networks, but should never be used in precision analog filtering or ADC voltage dividers.
Can a 3 band resistor colour code be read backwards?
No, reading backwards will yield a mathematically invalid or highly improbable value. For example, a 470Ω resistor is Yellow-Violet-Brown. If you read it backwards (Brown-Violet-Yellow), you get 170,000Ω (170kΩ). Because 17 is not a standard E24 multiplier base, you can immediately recognize the reading direction is wrong. Always verify that the first two digits form a standard E-series base number.
What is the difference between a 3 band and 4 band resistor colour code?
The physical component might look similar, but a 4-band resistor includes a dedicated tolerance band (usually Gold for ±5% or Silver for ±10%) as the fourth ring. A 3 band resistor colour code only has three rings, implying a wider ±20% tolerance. If you are holding a component with four rings, you must use the 4-band decoding logic, where the third ring is the multiplier and the fourth is the tolerance. For a comprehensive breakdown of higher-precision components, refer to the Vishay Resistor Color Code Guide.
