The marking is an identifier printed on the surface of a surface-mount resistor, which includes information such as the resistance value and tolerance.
Understanding these basic marking interpretation methods can greatly improve the efficiency of electronic circuit maintenance and debugging. Here are some common rules for interpreting surface-mount resistor markings:
1. Three-digit and Four-digit Numeric Markings
The digits at the beginning represent the significant value, and the last digit indicates the power of 10. Their product is the resistance value, for example:
- Three-digit numeric marking:
The first two digits represent the significant figures of the resistance value, and the third digit represents the power of 10. For instance, a resistor marked as 683 has a resistance value of 68*103 = 68kΩ.
Resistors with three-digit numeric markings typically have a tolerance of 5%.
* The commonly used E-24 series standard resistors follow this rule, see: Common Standard Resistor Value Table - Four-digit numeric marking:
The first three digits represent the significant figures of the resistance value, and the fourth digit represents the power of 10. For example, a resistor marked as 1502 has a resistance value of 150*102 = 15kΩ.
Resistors with four-digit numeric markings typically have a tolerance of 1%.
A common mistake for beginners: resistors with a trailing zero, such as 100, represent 10*100 = 10Ω, not 100Ω. // Don't ask how I know
2. EIA-96 Standard Code
Some high-precision surface-mount resistors may have a marking that includes a letter suffix, such as 30C or 34D, commonly found in 0603 packages. These markings usually follow the EIA-96 series standard, with a tolerance generally of ±1%.
The letter at the end represents the multiplier:
| Code | A | B | C | D | E | F | G | H | X/R | Y/S | Z/T |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Multiplier | 100 | 101 | 102 | 103 | 104 | 105 | 106 | 107 | 10-1 | 10-2 | 10-3 |
The first two digits represent the resistance value, with a base range consistent with the E96 series, totaling 96 types, which are not listed one by one here. If needed, you can refer to a table to confirm the specific base resistance value: EIA-96 Resistor Marking Comparison Table
The base represented by the numeric code and the multiplier represented by the letter code, their product is the resistance value, for example: the resistance value of 86D is calculated as 768*103 = 768kΩ.
3. Special Markings
- Markings with the letter R: When the marking includes the letter R, R represents the decimal point. For example, a resistor marked as 49R9 has a resistance value of 49.9Ω.
- 0Ω resistors: Manufacturers generally represent this with a single "0", and some may mark it as "000". It's worth noting that the character "0" often appears as a rectangle like "▯", and the tolerance accuracy cannot be determined by the number of digits.
- Markings with the letter M or L: The letter represents the decimal point and the unit is mΩ. For example, 5M1 = 5.1mΩ, 91L0 = 91mΩ.Note
- Three-digit markings starting with the letter V (Vxx): The unit is mΩ. For example, V05 = 5mΩ, V33 = 33mΩ.Note
For resistors with mΩ units, there seems to be no very unified marking standard among manufacturers. When encountering special markings, it is recommended to refer to the manufacturer's specifications and use actual measurements for accuracy.
4. Marking Reverse Lookup Tool
If you encounter an unfamiliar marking, you can use the tool on this site for reverse lookup to confirm: Resistor Marking Finder