About this calculator
Surface-mount resistors are too small for colour bands, so they carry printed codes instead. Four schemes are in common use, and one of them — EIA-96 — deliberately does not spell out the value, which is why a resistor marked 68C turns out to be 49.9 kΩ.
This decoder handles all four in both directions: paste in a marking to get the resistance, or enter a resistance to see what it would be printed as.
How it works
The 3-digit scheme is the most common. The first two digits are significant figures and the third is a power of ten, so 103 is 10 × 10³ = 10 kΩ. These are conventionally 5% parts.
The 4-digit scheme extends that to three significant figures for tighter tolerances: 1002 is 100 × 10² = 10 kΩ, the same value but marked on a 1% part.
R notation covers values below 10 Ω, where the digit schemes run out of room. The letter R stands in for the decimal point: 4R7 is 4.7 Ω and R047 is 0.047 Ω.
EIA-96 packs a 1% value into three characters. The two digits are an index into the 96-value E96 series rather than the value itself, and the letter is a multiplier. So 68C means "the 68th E96 value, which is 499" times 100 — 49.9 kΩ. It is compact and completely opaque until you know the trick.
A resistor marked 000 or 0 is a zero-ohm link — a wire bridge in resistor form, used to jump traces on a single-sided board or to make a track option.
Worked example
You have pulled three unmarked-looking resistors off a board: one reads 472, one reads 1003, and one reads 01C.
- 472 → 47 × 10² = 4700 Ω = 4.7 kΩ (5% part)
- 1003 → 100 × 10³ = 100000 Ω = 100 kΩ (1% part)
- 01C → E96 value #1 is 100, letter C is ×100
- 01C → 100 × 100 = 10000 Ω = 10 kΩ (1% part)
4.7 kΩ, 100 kΩ and 10 kΩ. The third one is the trap — read as a plain number, 01C looks like it should be near 1 Ω.
Practical notes
- The marking carries no tolerance information. By convention 3-digit codes are 5% parts and 4-digit or EIA-96 codes are 1%, but that is a convention, not a rule.
- 0402 and smaller packages are often completely unmarked — there is simply no room. Measuring is the only option, and measuring in-circuit reads the whole network, not the one part.
- EIA-96 letters have alternates between manufacturers: Y and R both mean ×0.01, X and S both mean ×0.1, B and H both mean ×10.
- A code is only a nominal value. A 1% part marked 49.9 kΩ is guaranteed between 49.4 kΩ and 50.4 kΩ.
- Some manufacturers use an underline beneath the code to distinguish EIA-96 from a plain 3-digit marking. Not all do.
- For high-value or unusual parts, always cross-check against the board's bill of materials if you have it. Reading codes off a photo is error-prone.
Frequently asked questions
How do I read SMD resistor codes?
For a 3-digit code, the first two digits are the value and the third is the number of zeros: 103 is 10 followed by three zeros, 10 kΩ. A 4-digit code works the same way with three significant digits.
What does 68C mean on a resistor?
49.9 kΩ. It is EIA-96, where the digits index the E96 series rather than giving the value directly — position 68 is 499 — and the letter C multiplies by 100.
What does 4R7 mean?
4.7 Ω. The R marks the decimal point, a scheme used for values below 10 Ω where the multiplier digit would otherwise have to be negative.
What is a 000 resistor for?
It is a zero-ohm jumper — a wire link in a resistor package. They let a single-sided board cross traces, and let one board serve several configurations by populating different links.
Why is my SMD resistor completely blank?
Packages of 0402 and below are usually unmarked because there is no room to print legibly. There is no way to identify them visually; measure with a meter, out of circuit.