A standard 1MΩ (1,000,000 ohms) through-hole resistor uses the color code Brown-Black-Green for a 4-band (5% or 10% tolerance) component, and Brown-Black-Black-Yellow for a 5-band (1% or 2% tolerance) precision component. For surface-mount (SMD) variants, the marking is 105. Below is the complete reference data, followed by critical high-voltage derating rules that standard color charts omit.
The 1M Resistor Color Code Reference Table
The table below covers the exact band sequences for 1 Megaohm resistors across the most common physical formats. Read the bands from left to right, starting from the side closest to the end cap. The tolerance band (Gold, Silver, or Brown) is always spaced slightly further apart or placed on the right.
| Format | Band 1 (Digit) | Band 2 (Digit) | Band 3 (Digit/Mult) | Band 4 (Multiplier/Tol) | Band 5 (Tolerance) | Nominal Value |
|---|---|---|---|---|---|---|
| 4-Band (5%) | Brown (1) | Black (0) | Green (×100k) | Gold (±5%) | N/A | 1,000,000 Ω |
| 4-Band (10%) | Brown (1) | Black (0) | Green (×100k) | Silver (±10%) | N/A | 1,000,000 Ω |
| 5-Band (1%) | Brown (1) | Black (0) | Black (0) | Yellow (×10k) | Brown (±1%) | 1,000,000 Ω |
| 5-Band (2%) | Brown (1) | Black (0) | Black (0) | Yellow (×10k) | Red (±2%) | 1,000,000 Ω |
| SMD 0805/1206 | Marking: 105 (10 × 105) | ±1% or ±5% | 1,000,000 Ω | |||
| SMD 0603 (EIA-96) | Marking: 01E (Code 01 = 100, E = 104) | ±1% | 1,000,000 Ω | |||
Standard Variants and Decoding the Multiplier
Resistor color codes are globally governed by IEC 60062 (published internationally and adopted as EN 60062 in Europe). In the US, you may still encounter references to the legacy EIA-RS-279 or MIL-SPEC standards on vintage military or aerospace equipment, but the color mappings for 1MΩ remain identical across all modern and legacy systems. The primary difference lies in the physical construction and the introduction of the 5-band system for tighter tolerances.
Understanding the 1MΩ Multiplier Math
The most common point of failure when reading a 1MΩ resistor is miscalculating the multiplier band. A 1MΩ resistor requires multiplying the base digits by either 100,000 or 10,000, depending on the band count:
- 4-Band System: The first two bands are digits (Brown=1, Black=0). The third band is the multiplier. To get 1,000,000 from 10, you must multiply by 100,000 (105). In the IEC 60062 standard, Green represents 105.
- 5-Band System: The first three bands are digits (Brown=1, Black=0, Black=0). The fourth band is the multiplier. To get 1,000,000 from 100, you must multiply by 10,000 (104). In the standard, Yellow represents 104.
Table Rows People Get Wrong and Faded Marking Fixes
When cross-referencing the table above, bench technicians frequently misidentify specific rows due to visual similarities in the color bands or degraded component coatings. Here is how to navigate the most common errors.
Rows and Bands People Get Wrong
- Confusing Green (105) with Blue (106) on 4-Band Resistors: Under warm LED bench lighting, the green multiplier band can easily look teal or blue. If you misread the third band as Blue, you are looking at a 10MΩ resistor (Brown-Black-Blue), not a 1MΩ resistor. Always verify with a digital multimeter (DMM) if the lighting is questionable.
- Reversing the 5-Band Sequence: Because a 1% tolerance 5-band resistor uses a Brown tolerance band, and Brown is also a valid digit band (1), readers sometimes start from the wrong end. If you read it backward, Brown-Yellow-Black-Black-Brown translates to 140Ω. Fix: Look for the physical gap. The tolerance band is always spaced slightly wider from the adjacent multiplier band.
- Misreading SMD '105' as 105 Ohms: Novices often read the SMD marking '105' literally. Remember that the 3-digit SMD code uses the last digit as a power-of-ten exponent. 10 × 105 = 1,000,000.
Safe Interpretation of Faded or Missing Markings
Carbon composition resistors—frequently found in vintage audio gear, old CRT flyback circuits, and early oscilloscope probes—are notorious for baking over decades. The clear epoxy coating yellows, and the brown and red bands degrade into an indistinguishable muddy orange. Furthermore, carbon comp resistors naturally drift high in value as they age and absorb moisture.
How to safely verify a faded 1MΩ resistor:
- De-energize and Discharge: 1MΩ resistors are often used in high-impedance voltage dividers or capacitor bleed networks. Turn off the power and use a high-voltage probe or a dedicated discharge tool to bleed any associated capacitors. A charged capacitor will feed voltage back through the 1MΩ resistor, frying your multimeter or shocking you.
- Isolate One Leg: Do not measure the resistor in-circuit. In a high-impedance 1MΩ network, parallel PCB leakage paths or adjacent components will skew your DMM reading. Desolder or lift one leg of the resistor off the PCB pad.
- Measure and Evaluate Drift: Set your DMM to the Megaohm range. If the reading is between 950kΩ and 1.05MΩ, the component is likely a standard 5% 1MΩ resistor in good health. If the reading is >1.2MΩ or fluctuating wildly, the carbon matrix has degraded. Replace it with a modern 1MΩ 1% metal film resistor, ensuring the new part's MWV rating exceeds the circuit's peak voltage.
For further reading on standard component markings and high-voltage derating curves, refer to the All About Circuits resistor color code guide and the Electronics Tutorials color code calculator. Always cross-reference specific component datasheets (such as the IEC 60062 standard documentation) when designing high-voltage analog front-ends where temperature coefficient (TCR) and voltage coefficient of resistance (VCR) can introduce measurement errors at the 1MΩ scale.
