RandoziSMD Resistor Code Decoder
The tiny number on a surface-mount resistor is a code, not a value. Type it and read the resistance, whether the code has three digits, four digits, an R for the decimal point or the letter system of the 1 % series.
| Code | Value | Scheme | Tolerance | Note |
|---|---|---|---|---|
| 472 | 4.7 kΩ | 3-digit | 5 % (usually) | Two digits, then the number of zeros. |
| 1002 | 10 kΩ | 4-digit | 1 % (usually) | Three digits, then the number of zeros. |
| 4R7 | 4.7 Ω | R notation | 5 % (3 characters) | R marks the decimal point. |
| 01C | 10 kΩ | EIA-96 | 1 % | Code 01 = 100, ×100. |
| 68X | 49.9 Ω | EIA-96 | 1 % | Code 68 = 499, ×0.1. |
How it works
- Read the characters printed on the resistor (use a magnifier; the code can be upside down).
- Type them in, one code per line or separated by spaces.
- Read the value and which marking scheme was recognised.
- Compare with a meter if the value matters: a worn or hot part can read differently.
What people use it for
Repairing a board
Identify a part marked 103 or 4R7 without a datasheet.
Sorting a parts bin
Decode a whole row of loose resistors at once and label the bags.
Reading a precision part
Turn a code such as 68X into 49.9 Ω instead of guessing.
Questions
- How are the codes read?
- Three digits: the first two are the value and the third is the number of zeros, so 472 is 47 followed by two zeros, 4,700 Ω or 4.7 kΩ. Four digits: three digits, then the zeros, so 1002 is 10 kΩ. With an R, the R is the decimal point: 4R7 is 4.7 Ω and R47 is 0.47 Ω. A single 0 or 000 is a zero-ohm link.
- What is EIA-96?
- A two-digit number from 01 to 96 picks a value from the standard 1 % (E96) series, such as 01 = 100 and 68 = 499. The letter after it is a multiplier: A ×1, B or H ×10, C ×100, D ×1,000, E ×10,000, F ×100,000, and X or S ×0.1, Y or R ×0.01, Z ×0.001. So 01C is 100 × 100 = 10 kΩ and 68X is 499 × 0.1 = 49.9 Ω. The 96 values are the standard E96 series; for a critical part, check the code against its maker's datasheet.
- Why is 47R not decoded as an EIA-96 code?
- 47R is also a valid EIA-96 code (3.01 Ω) as well as the usual way to write 47 Ω. The tool reads it as 47 Ω, as is customary, and says so in the note. When in doubt, measure the part.
- Is the tolerance exact?
- No. 3-digit codes are usually 5 % parts and 4-digit and EIA-96 codes usually 1 %, but this is a habit, not a rule: the marking does not state the tolerance. Check the datasheet for the real figure. Up to 200 codes are read at a time; nothing is sent anywhere.