What are SMD codes
Surface-mount resistors and capacitors are too small to print a full value on, so manufacturers use short codes. A few digits, sometimes with a letter, encode the resistance in ohms or the capacitance in picofarads. There is more than one convention, and a bare 3-digit code can be valid as both a resistor and a capacitor, so it helps to know which rule applies to the part in front of you.
SMD resistor code formats
These are the four resistor codings you will meet most often, with a worked example of each.
| Format | Rule | Example | Value |
|---|---|---|---|
| 3-digit | Two significant digits, third is the multiplier | 472 | 47 x 10^2 = 4.7 kOhm |
| R-notation | R marks the decimal point, for values under 100 ohms | 4R7 | 4.7 Ohm |
| 4-digit | Three significant digits, fourth is the multiplier | 4701 | 470 x 10^1 = 4.7 kOhm |
| EIA-96 | Two-digit table index plus a multiplier letter | 01A | 100 x 1 = 100 Ohm |
How to read a 3-digit code
Take the resistor code 472. The first two digits, 47, are the significant figures. The third digit, 2, is the multiplier, meaning the number of zeros to add. So the value is 47 followed by 2 zeros, which is 4,700 ohms, written as 4.7 kOhm. A code of 100 is 10 followed by no zeros, which is 10 ohms, not 100 ohms. The same rule on a ceramic capacitor gives a value in picofarads instead of ohms.
R-notation and small values
For values below 100 ohms, the letter R stands in for the decimal point. This is clearer than trying to print a tiny leading decimal. So 4R7 is 4.7 ohms, R47 is 0.47 ohms, and R100 is 0.1 ohms. On a 4-character precision part the same idea applies, with three significant figures around the R.
The EIA-96 code
EIA-96 is used on 1% precision resistors. It packs three significant figures into two digits plus a letter. The two digits are an index into the 96-value table below, and the letter is the multiplier. For example, 68X reads as code 68, which the table maps to 499, times the X multiplier of 0.1, giving 49.9 ohms.
| Letter | Multiplier |
|---|---|
| Z | 0.001 |
| Y or R | 0.01 |
| X or S | 0.1 |
| A | 1 |
| B or H | 10 |
| C | 100 |
| D | 1000 |
| E | 10000 |
| F | 100000 |
SMD capacitor codes
Ceramic capacitor codes follow the same 3-digit pattern as resistors, but the result is in picofarads. The code 104 is 10 followed by 4 zeros, which is 100,000 pF, equal to 100 nF or 0.1 uF. A short code such as 220 is 22 pF, and 471 is 470 pF. A trailing letter, when present, gives the tolerance: J is plus or minus 5 percent, K is plus or minus 10 percent, and M is plus or minus 20 percent.
Zero-ohm jumpers
A code of all zeros, such as 000 or 0000, marks a zero-ohm jumper. This is a solid link used to bridge a gap on a board, not a resistor with a real value. It is a common way to make a wire link fit the same pick-and-place process as the rest of the parts.
Frequently asked questions
How do I read a 3-digit SMD resistor code?
The first two digits are the significant figures and the third digit is the number of zeros to add, that is the power-of-ten multiplier. For example, 472 means 47 followed by 2 zeros, which is 4,700 ohms or 4.7 kOhm. A code of 100 means 10 followed by 0 zeros, which is 10 ohms.
What does a 472 resistor mean?
A resistor marked 472 is 4.7 kOhm. The 47 is the significant part and the 2 is the multiplier, so the value is 47 times 10 to the power of 2, which is 4,700 ohms. The same 472 marking on a ceramic capacitor would mean 4,700 picofarads, or 4.7 nF.
What does the R mean in a resistor code like 4R7?
The letter R marks the position of the decimal point and is used for values below 100 ohms. So 4R7 is 4.7 ohms, R47 is 0.47 ohms, and R100 is 0.1 ohms. This avoids the ambiguity of a leading decimal point that can be hard to print on a tiny part.
What is an EIA-96 resistor code?
EIA-96 is a compact code for 1% precision resistors. It uses two digits plus one letter. The two digits are an index into a 96-value table that gives 3 significant figures, and the letter is the multiplier. For example, 01A is 100 ohms and 68X is 49.9 ohms, since code 68 maps to 499 and the letter X means multiply by 0.1.
How do I read an SMD ceramic capacitor code?
A 3-digit ceramic capacitor code works like a resistor code but the result is in picofarads. The first two digits are significant and the third is the multiplier. So 104 is 10 followed by 4 zeros, which is 100,000 pF, equal to 100 nF or 0.1 uF. A trailing letter, if present, is the tolerance, for example K means plus or minus 10 percent.
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