Reading SMD Resistor Codes: 3-Digit, 4-Digit and EIA-96
Unlike the color bands on through-hole (THT) resistors, most surface-mount (SMD) resistors have a small numeric code printed on them. This code gives the resistor's value in ohms — but because there are a few different systems, it can be confusing at first glance. This article focuses less on what an SMD resistor is and more on how to read these codes in practice.
3-digit code (the most common)
The first two digits are the significant figures, and the third digit is the multiplier (how many zeros to add). The result is in ohms:
| Code | How to read it | Value |
|---|---|---|
| 103 | 10 + 3 zeros | 10,000 Ω = 10 kΩ |
| 472 | 47 + 2 zeros | 4,700 Ω = 4.7 kΩ |
| 220 | 22 + 0 zeros | 22 Ω |
| 105 | 10 + 5 zeros | 1,000,000 Ω = 1 MΩ |
Decimal values with 'R'
For values below 1 Ω or with a decimal, the letter R is used instead of a decimal point. The position of the R marks the decimal:
- 4R7 → 4.7 Ω
- R47 → 0.47 Ω
- 0R5 → 0.5 Ω
The zero-ohm jumper
An SMD resistor marked only 0 (or sometimes 000) isn't really a resistor; it's a jumper. That is, it connects two points with nearly zero resistance. In manufacturing it's used to make a connection suitable for automated assembly instead of a wire jumper.
4-digit code (precision resistors)
For 1% and tighter-tolerance resistors, four digits are used: the first three digits are the significant figures, and the last digit is the multiplier. This allows more precise values to be encoded:
| Code | How to read it | Value |
|---|---|---|
| 4701 | 470 + 1 zero | 4,700 Ω = 4.7 kΩ |
| 1002 | 100 + 2 zeros | 10,000 Ω = 10 kΩ |
| 1R00 | decimal with R | 1.00 Ω |
The EIA-96 system (2 digits + letter)
To save space on very small precision resistors, EIA-96 is used: two digits are a code number (corresponding to a value in the E96 series), and the letter indicates the multiplier. So the digits aren't the value directly; they're interpreted by looking at a table.
| Letter | Multiplier | Example |
|---|---|---|
| Y / R | ×0.01 | — |
| X / S | ×0.1 | — |
| A | ×1 | 01A = 100 Ω |
| B / H | ×10 | 01B = 1 kΩ |
| C | ×100 | 01C = 10 kΩ |
For example 01A: the code "01" corresponds to 100 in the E96 table, and the letter "A" corresponds to a ×1 multiplier → 100 Ω. In practice you need an EIA-96 reference table to read a value precisely in this system.
Which system does the package size imply?
Which code system you'll encounter depends largely on package size and tolerance. A rough general tendency:
- 0805 and up, 5%: mostly a 3-digit code is printed.
- 0603/0805, 1%: a 4-digit code or EIA-96 appears.
- 0402 and smaller: text usually doesn't fit; no code is printed.
So when reading a code on a board, looking at the package size gives a quick hint about which system to expect.
Common mistakes
- Mixing up the 3- and 4-digit systems: in the 4-digit system the multiplier is the LAST digit; reading it with 3-digit logic gives the wrong result.
- Reading EIA-96 numerically: the "01" in "01A" is a table code, not the value directly.
- Mistaking a '0' jumper for a resistor: when measuring in-circuit, don't read zero and assume a fault; it's a jumper.
- Ignoring the R position: R47 and 4R7 are entirely different values.
Frequently asked questions
Are there SMD resistors with no printing at all?
Yes. On very small packages (e.g. 0402 and below), text doesn't fit so no code is printed; you can only find the value by measuring or from the assembly documentation.
Can I tell the tolerance from the code?
Not directly. Generally a 3-digit code is used on 5% resistors, and 4-digit and EIA-96 on 1% and tighter parts; the exact tolerance is stated in the datasheet.
Is measuring with a multimeter safer than the code?
Measuring out of circuit is the most precise way. In-circuit, parallel paths can skew the measurement, so reading the code is a practical piece of prior knowledge.
Conclusion
SMD resistor codes come down to four basic systems: 3-digit (with multiplier), decimal with 'R', 4-digit (precision) and EIA-96 (code + letter). Once you know the system, reading becomes a few-second task; when unsure, verify the part out of circuit with a multimeter. You can find current supplier offers for SMD resistors of the right value with search and compare alternatives. When placing SMD parts on the board, our reflow SMD soldering article is also useful.