How do I read the code on an SMD resistor?
Surface-mount (SMD) resistors are too small for colour bands, so their value is printed as a short code. There are a few systems, and you can tell them apart by how the code looks.
- Turn the board so the code reads the right way up. Use a magnifier or your phone camera zoomed in.
- Count the characters. Three digits, four digits, digits with an R, or two digits and a letter.
- Type it into the calculator above. It says which system it is, shows the working and gives the value.
- Measure when it matters. If the value looks wrong for the circuit, check the part with a multimeter, out of the circuit.
Which code system is it?
Every system writes a value in a few characters. The number of digits also hints at the tolerance.
| System | Looks like | How to read it | Example | Tolerance |
|---|---|---|---|---|
| 3-digit | Three digits | Two digits, then the number of zeros. | 472 = 4.7 kΩ | Usually ±5% |
| 4-digit | Four digits | Three digits, then the number of zeros. | 4701 = 4.7 kΩ | Usually ±1% |
| R notation | Digits with an R | R is the decimal point. | 4R7 = 4.7 Ω | Not in the code |
| EIA-96 | Two digits and a letter | Position in the E96 list, then a multiplier letter. | 01C = 10 kΩ | ±1% |
| Jumper | 0, 000 or 0R | Zero ohms: a plain link. | 000 = 0 Ω | — |
3-digit codes
The first two digits are the value, the third is how many zeros follow. 472 is 47 and two zeros: 4,700 Ω, or 4.7 kΩ. 220 is 22 and no zeros: 22 Ω. Values below 10 Ω use R notation instead, like 4R7.
4-digit codes
The same idea with three value digits, for 1% parts. 4701 is 470 and one zero: 4.7 kΩ. 1002 is 100 and two zeros: 10 kΩ. Below 100 Ω the R is used: 49R9 is 49.9 Ω.
EIA-96 codes
Small 1% parts have room for only three characters, so the two digits point to a value in the E96 list (table below) and the letter multiplies it. 68X is 499 × 0.1 = 49.9 Ω.
What code does a common value have?
Each value in every system. A value in brackets is the nearest one that system can write: 4.7 kΩ is not in the E96 list, so the nearest EIA-96 code is 4.75 kΩ.
| Value | 3-digit code | 4-digit code | EIA-96 code |
|---|---|---|---|
| 1 Ω | 1R0 | 1R00 | 01Y |
| 4.7 Ω | 4R7 | 4R70 | 66Y (≈ 4.75 Ω) |
| 10 Ω | 100 | 10R0 | 01X |
| 22 Ω | 220 | 22R0 | 34X (≈ 22.1 Ω) |
| 47 Ω | 470 | 47R0 | 66X (≈ 47.5 Ω) |
| 100 Ω | 101 | 1000 | 01A |
| 220 Ω | 221 | 2200 | 34A (≈ 221 Ω) |
| 330 Ω | 331 | 3300 | 51A (≈ 332 Ω) |
| 470 Ω | 471 | 4700 | 66A (≈ 475 Ω) |
| 1 kΩ | 102 | 1001 | 01B |
| 2.2 kΩ | 222 | 2201 | 34B (≈ 2.21 kΩ) |
| 4.7 kΩ | 472 | 4701 | 66B (≈ 4.75 kΩ) |
| 10 kΩ | 103 | 1002 | 01C |
| 22 kΩ | 223 | 2202 | 34C (≈ 22.1 kΩ) |
| 47 kΩ | 473 | 4702 | 66C (≈ 47.5 kΩ) |
| 100 kΩ | 104 | 1003 | 01D |
| 1 MΩ | 105 | 1004 | 01E |
What does each EIA-96 code stand for?
The two digits of an EIA-96 code and the value they stand for. Multiply by the letter below: 01C = 100 × 100 = 10 kΩ.
| Code | Value | Code | Value | Code | Value | Code | Value | Code | Value | Code | Value |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 01 | 100 | 17 | 147 | 33 | 215 | 49 | 316 | 65 | 464 | 81 | 681 |
| 02 | 102 | 18 | 150 | 34 | 221 | 50 | 324 | 66 | 475 | 82 | 698 |
| 03 | 105 | 19 | 154 | 35 | 226 | 51 | 332 | 67 | 487 | 83 | 715 |
| 04 | 107 | 20 | 158 | 36 | 232 | 52 | 340 | 68 | 499 | 84 | 732 |
| 05 | 110 | 21 | 162 | 37 | 237 | 53 | 348 | 69 | 511 | 85 | 750 |
| 06 | 113 | 22 | 165 | 38 | 243 | 54 | 357 | 70 | 523 | 86 | 768 |
| 07 | 115 | 23 | 169 | 39 | 249 | 55 | 365 | 71 | 536 | 87 | 787 |
| 08 | 118 | 24 | 174 | 40 | 255 | 56 | 374 | 72 | 549 | 88 | 806 |
| 09 | 121 | 25 | 178 | 41 | 261 | 57 | 383 | 73 | 562 | 89 | 825 |
| 10 | 124 | 26 | 182 | 42 | 267 | 58 | 392 | 74 | 576 | 90 | 845 |
| 11 | 127 | 27 | 187 | 43 | 274 | 59 | 402 | 75 | 590 | 91 | 866 |
| 12 | 130 | 28 | 191 | 44 | 280 | 60 | 412 | 76 | 604 | 92 | 887 |
| 13 | 133 | 29 | 196 | 45 | 287 | 61 | 422 | 77 | 619 | 93 | 909 |
| 14 | 137 | 30 | 200 | 46 | 294 | 62 | 432 | 78 | 634 | 94 | 931 |
| 15 | 140 | 31 | 205 | 47 | 301 | 63 | 442 | 79 | 649 | 95 | 953 |
| 16 | 143 | 32 | 210 | 48 | 309 | 64 | 453 | 80 | 665 | 96 | 976 |
| Letter | Multiply by | Example |
|---|---|---|
| Z | × 0.001 | 01Z = 0.1 Ω |
| Y or R | × 0.01 | 01Y = 1 Ω |
| X or S | × 0.1 | 01X = 10 Ω |
| A | × 1 | 01A = 100 Ω |
| B or H | × 10 | 01B = 1 kΩ |
| C | × 100 | 01C = 10 kΩ |
| D | × 1,000 | 01D = 100 kΩ |
| E | × 10,000 | 01E = 1 MΩ |
| F | × 100,000 | 01F = 10 MΩ |
Makers use either letter of a pair (Y or R, X or S, B or H). A code like 68R can also be R notation (68 Ω); the calculator shows both readings.
Can I see a few worked out?
Worked out by the same code as the calculator above.
472 = 4.7 kΩ
47 × 10² = 4,700 Ω (the last digit 2 is the number of zeros)
Usually ±5%1002 = 10 kΩ
100 × 10² = 10,000 Ω (the last digit 2 is the number of zeros)
Usually ±1%4R7 = 4.7 Ω
R is the decimal point: 4.7 = 4.7 Ω
Tolerance not in the code01C = 10 kΩ
code 01 = 100, letter C = × 10², so 100 × 10² = 10,000 Ω
Usually ±1%What do people often get wrong?
Reading 100 as 100 Ω
The last digit is a count of zeros. 100 is 10 Ω; 101 is 100 Ω.
Reading it upside down
Some codes still make sense rotated, like 601 and 109. Turn the board until the text reads normally.
Mixing up capacitors
Ceramic capacitors often have no print at all, and other parts use similar codes. A resistor is usually black with white print; check the board label (R1, R2…).
Measuring in the circuit
Other parts in parallel change the reading. Lift one end of the resistor or measure a spare part.
Short answers to common questions
What does 103 mean on an SMD resistor?
103 is a 3-digit code. The first two digits are 10 and the last digit says how many zeros to add: 10 followed by 3 zeros is 10,000 Ω, so 10 kΩ.
Is a resistor marked 100 a 100 ohm resistor?
No. 100 means 10 followed by no zeros, so 10 Ω. A 100 Ω part is marked 101 (3-digit) or 1000 (4-digit).
What does the R mean in 4R7?
R marks the decimal point. 4R7 is 4.7 Ω, R10 is 0.1 Ω and 49R9 is 49.9 Ω. It is used for small values, where a zeros count would not work.
What is an EIA-96 code like 01C?
It is a short code for 1% resistors that are too small for four digits. The two digits are a position in the E96 list of standard values (01 is 100, 96 is 976) and the letter is the multiplier (C is ×100). So 01C is 100 × 100 = 10 kΩ.
What does 000 or 0 mean on an SMD resistor?
A code of 0, 00, 000 or 0000 (or 0R) marks a zero-ohm jumper. It is a plain link in a resistor's body, used to join two tracks on a board.
How do I know if a code is 3-digit, 4-digit or EIA-96?
Count the characters. Three digits is the 3-digit system, four digits is the 4-digit system, two digits and a letter is EIA-96, and a code with R in it is R notation.
Why does my SMD resistor have no code at all?
The smallest parts (0402 and smaller) are usually not marked: there is no room. Measure them with a multimeter, or keep them on their labelled reel or strip.
Can the code be read upside down?
Yes, and some codes still look valid upside down. Turn the board so the text reads normally, and if the value seems wrong for the circuit, measure the part out of circuit.