The 4-band colour code for a 6.8 kΩ (6800 ohm) resistor is Blue, Grey, Red, Gold. For a 5-band 1% precision metal film resistor, the sequence is Blue, Grey, Black, Brown, Brown. In surface-mount (SMD) format, the equivalent marking is 682 (5%) or 6801 (1%).
| Format / Tolerance | Band 1 (Digit) | Band 2 (Digit) | Band 3 (Digit/Mult) | Band 4 (Multiplier/Tol) | Band 5 (Tolerance) | SMD Equivalent |
|---|---|---|---|---|---|---|
| 4-Band (±5% Carbon) | Blue (6) | Grey (8) | Red (×100) | Gold (±5%) | N/A | 682 |
| 5-Band (±1% Metal) | Blue (6) | Grey (8) | Black (0) | Brown (×10) | Brown (±1%) | 6801 |
| 5-Band (±5% Metal Oxide) | Blue (6) | Grey (8) | Black (0) | Brown (×10) | Gold (±5%) | 682 |
| 6-Band (±1% + Tempco) | Blue (6) | Grey (8) | Black (0) | Brown (×10) | Brown (±1%) | N/A (Add Red for 50ppm) |
| SMD Thick Film (±5%) | 682 (68 × 10²) | N/A | 682 | |||
Decoding the 6.8 k Resistor Colour Code Bands
To understand why a 6.8 kΩ resistor uses these specific colours, you have to look at the Vishay standard resistor value tables and the E-series system. The number 6.8 is not arbitrary; it is the 11th value in the E12 series (which provides 12 logarithmically spaced values per decade). Because 6.8 is a base E12 value, you will find it in virtually every resistor kit, whether it is a cheap 5% carbon film or a high-precision 0.1% metal foil resistor.
In the standard IEC 60062 colour code system, the bands are read from left to right, starting from the band closest to the lead. For the 4-band 6.8 kΩ variant:
- Blue (Band 1): Represents the first significant digit, 6.
- Grey (Band 2): Represents the second significant digit, 8.
- Red (Band 3): The multiplier. Red means ×10² (or ×100). So, 68 × 100 = 6800 ohms (6.8 kΩ).
- Gold (Band 4): The tolerance. Gold indicates ±5%, meaning the actual measured resistance can safely fall anywhere between 6.46 kΩ and 7.14 kΩ.
For the 5-band 1% variant, the system inserts a third digit band to accommodate tighter tolerances. The sequence becomes Blue (6), Grey (8), Black (0), followed by a Brown multiplier (×10¹), yielding 680 × 10 = 6800 ohms. The final Brown band indicates a ±1% tolerance (6.732 kΩ to 6.868 kΩ).
Component vs. Mains Standards: IEC 60062 vs. NEC & Old UK
A dangerous and frequent point of confusion for hobbyists crossing over from home wiring to bench electronics is assuming that mains wiring colour standards apply to electronic components. They do not. Mixing these domains can lead to catastrophic miswiring or misdiagnosis.
Resistors globally adhere to IEC 60062 (which evolved from the US EIA-RS-279 and old MIL-SPEC standards). This standard is universal for components. Mains wiring, however, is strictly regional and governed by entirely different bodies, such as the NFPA 70 (NEC) in the US or the IET Wiring Regulations in the UK.
| Colour | IEC 60062 (Resistor Band) | IEC 60446 (EU/UK Mains) | Old UK Mains (Pre-2004) | NEC / NFPA 70 (US Mains) |
|---|---|---|---|---|
| Blue | Digit: 6 | Neutral | N/A (Not standard) | N/A (Not standard for AC) |
| Brown | Digit: 1 / Mult: ×10 | Line (Live/Hot) | N/A | N/A |
| Red | Digit: 2 / Mult: ×100 | N/A | Line (Live/Hot) | Hot (Phase 1 / Switched) |
| Black | Digit: 0 / Mult: ×1 | N/A | Neutral | Hot (Phase 2 / Line) |
| Green/Yellow | N/A (Not used in 4/5 band) | Earth (Ground) | Earth (Ground) | Bare or Green (Ground) |
If you are repairing a vintage British amplifier built in the 1980s, you will encounter Old UK wiring colours (Red=Live, Black=Neutral) inside the chassis, but the resistors on the PCB will still use the universal IEC 60062 colour code. Always verify the domain—component or mains—before interpreting a colour.
Rows People Get Wrong & Faded Marking Recovery
Even experienced technicians misread resistor bands under poor lighting or when dealing with aged components. Here are the most common pitfalls specific to the 6.8 kΩ value and how to resolve them.
The Red vs. Orange Multiplier Trap
The most common mistake when reading a 4-band 6.8 kΩ resistor is confusing the Red multiplier (×100) with an Orange multiplier (×1000). Under warm incandescent bench lighting or on a sun-faded PCB, Red can easily look Orange. If you misread the third band as Orange, you will log the component as 68 kΩ instead of 6.8 kΩ. This 10x error will completely alter the bias point of a transistor circuit or the cutoff frequency of an RC filter. Always verify the multiplier band under neutral white (5000K) LED lighting.
Reading Backwards
Beginners sometimes read the bands from right to left. The universal rule to prevent this is to locate the tolerance band first. Gold and Silver are only used for tolerance (and occasionally temperature coefficient in 6-band resistors); they are never used for significant digits or multipliers. If you see a Gold band on the far right, start reading from the left. If a resistor has no Gold or Silver band (e.g., a 5-band 2% resistor where the tolerance band is Red), look for the wider gap between the multiplier and tolerance bands, or use a multimeter to establish the correct orientation.
Safe Interpretation of Faded or Burnt Markings
Carbon composition and older carbon film resistors subjected to high ambient heat (such as those located near power transistors or vacuum tube plates) suffer from thermal discoloration. The resistor body may turn dark brown, and the Red multiplier band can bake into a muddy, unreadable grey-brown.
Recovery Protocol:
- Visual Estimation: If the first two bands are clearly Blue and Grey, you know the base digits are 68. The value is likely 68Ω, 680Ω, 6.8kΩ, or 68kΩ.
- Out-of-Circuit Measurement: Desolder at least one leg of the resistor. Measure it with a digital multimeter (DMM). If it reads ~6.75 kΩ, your 6.8 kΩ identification is confirmed.
- In-Circuit Measurement Caveat: If you cannot desolder the component, measure it in-circuit but understand that parallel circuit paths will always make the DMM read a lower value than the actual resistor. If your in-circuit DMM reads 5.2 kΩ, the 6.8 kΩ resistor might be perfectly fine (shunted by a parallel 22 kΩ path). However, if the in-circuit reading is higher than 6.8 kΩ, or reads open (OL), the resistor has drifted from thermal stress and must be replaced.
When replacing a faded 6.8 kΩ carbon film resistor in a vintage audio or RF circuit, consider upgrading to a 1% metal film resistor (Blue-Grey-Black-Brown-Brown). Metal film generates less thermal noise and is far more resistant to the thermal fading that destroyed the original component's markings.
