SMD resistor codes: reading three-digit, four-digit, R and EIA-96 markings
A chip resistor has no room for colour bands, so its value is printed on top, and over the years four conventions have grown up. Three digits (472) are two significant figures and a count of zeros, the 5 % parts. Four digits (4701) add a third figure for the 1 % parts. An R or m in the code (4R7, R010) stands for the decimal point. And EIA-96 (68C) packs a 1 % value into three characters: two digits that index the E96 series and a letter multiplier. All zeros is a jumper. This calculator reads any of them, tells you the value, the tolerance the scheme implies and the series, writes the same value in every other code, and shows the chip and the package sizes to scale.
How to use the SMD code calculator
- Type the marking exactly as printed: 472, 1002, 4R7, R010, 68C, 000. Case does not matter.
- Or type a value (4.7k, 0.22, 49.9k) to see it written in every code that can express it; click a code to read it back.
- The drawing shows the chip with the parts of the code explained, and the panel the value, the tolerance, the series and the sizes. The EIA-96 table tab has all 96 codes.
Three digits: two figures and a multiplier
value = d₁d₂ × 10d₃
The first two digits are the significant figures, the third the number of zeros to add: 472 is 47 followed by two zeros, 4 700 Ω; 103 is 10 000 Ω; 100 is 10 Ω; 1R0 would be 1 Ω (see below). It is the same logic as the first three colour bands, and it covers the E24 (5 %) values, which have two significant figures. An underline or a bar over a three-digit code marks a 1 % part that happens to be an E24 value.
Four digits: three figures for 1 % parts
value = d₁d₂d₃ × 10d₄
E96 values have three significant figures (4.75 kΩ, 49.9 kΩ), so 1 % parts carry four digits: 4751 is 475 followed by one zero, 4 750 Ω; 1002 is 10 kΩ; 4700 is 470 Ω (470 followed by no zeros). Used on 0805 and larger, where there is room.
R and m: the decimal point
A printed dot would vanish, so a letter takes its place: 4R7 is 4.7 Ω, R22 is 0.22 Ω, 0R5 is 0.5 Ω, 10R0 is 10.0 Ω on a 1 % part. Current-sense resistors below an ohm use m for milliohms: R010 and 10m0 both mean 10 mΩ, 2m2 is 2.2 mΩ. Some makers use L for milliohms instead; the letter is always where the point would go.
EIA-96: a 1 % value in three characters
value = E96[d₁d₂] × multiplier(letter)
On an 0603 there is room for only three characters, yet 1 % values need three figures. EIA-96 solves it by numbering the 96 values of the E96 series from 01 (100) to 96 (976) and following the number with a multiplier letter: Z ×0.001, Y or R ×0.01, X or S ×0.1, A ×1, B or H ×10, C ×100, D ×1 000, E ×10 000, F ×100 000. So 01A is 100 Ω, 01C is 10 kΩ, 68C is 499 × 100 = 49.9 kΩ, 22B is 165 × 10 = 1.65 kΩ. The trap is that the digits are a position in the table, not a value: 10B is not 100 Ω but 124 × 10 = 1.24 kΩ.
| Code | Digits → E96 value | Letter → multiplier | Resistance |
|---|---|---|---|
| 01A | 01 → 100 | A = ×1 | 100 Ω |
| 01C | 01 → 100 | C = ×100 | 10 kΩ |
| 10B | 10 → 124 | B = ×10 | 1.24 kΩ |
| 22B | 22 → 165 | B = ×10 | 1.65 kΩ |
| 68C | 68 → 499 | C = ×100 | 49.9 kΩ |
| 96E | 96 → 976 | E = ×10,000 | 9.76 MΩ |
| 01Y | 01 → 100 | Y = ×0.01 | 1 Ω |
| 47X | 47 → 301 | X = ×0.1 | 30.1 Ω |
Sizes and power
Chip sizes are named by their length and width in hundredths of an inch (0805 is 0.08 × 0.05 in) or, confusingly, in tenths of a millimetre (the same part is 2012 metric). The power rating grows with the size and depends on the board's copper: the figures below are the usual catalogue values. 0402 and smaller are too small to print on; 0603 carries three characters, 0805 and up three or four.
| Imperial | Metric | Size | Typical power | Marking |
|---|---|---|---|---|
| 0201 | 0603 | 0.6 × 0.3 mm | 0.05 W | none |
| 0402 | 1005 | 1 × 0.5 mm | 0.063 W | none |
| 0603 | 1608 | 1.6 × 0.8 mm | 0.1 W | 3 characters |
| 0805 | 2012 | 2 × 1.25 mm | 0.125 W | 3 or 4 characters |
| 1206 | 3216 | 3.2 × 1.6 mm | 0.25 W | 3 or 4 characters |
| 1210 | 3225 | 3.2 × 2.5 mm | 0.5 W | 3 or 4 characters |
| 2010 | 5025 | 5 × 2.5 mm | 0.75 W | 3 or 4 characters |
| 2512 | 6332 | 6.3 × 3.2 mm | 1 W | 3 or 4 characters |
Your marking, step by step
- Scheme: 472 is a three-digit code.
- Reading: 47 followed by 2 zeros: 47 × 10^2.
- Value: 4.7 kΩ, ±5 % (usually), a E6 value; also written 4701.
Worked example: 472, 4701 and 68C
An 0805 marked 472 is 47 followed by 2 zeros: 4.7 kΩ, a 5 % E24 value; as a 1 % part it would be printed 4701 (470 followed by no zeros), and on an 0603 it could not be EIA-96, because 4.70 is not in the E96 list (4.64 and 4.75 are). A part marked 4701 is 470 followed by one zero, 4.7 kΩ at 1 %. And an 0603 marked 68C is EIA-96: code 68 is the 68th E96 value, 499, and C multiplies by 100, so 49.9 kΩ, which a bigger part would print as 4992. A chip marked R010 is 0.010 Ω, a 10 mΩ current-sense resistor, and one marked 000 is a jumper.
Questions
Is 100 the same as 101?
No: 100 is 10 followed by no zeros, 10 Ω; 101 is 10 followed by one zero, 100 Ω. The last digit is always the zero count.
What does a letter at the end mean?
With two digits before it, EIA-96: the digits index the E96 table and the letter multiplies. 47R, with the R in the point's position, is 47 Ω, but it is rarely printed that way.
Why is my chip blank?
0402 and smaller have no room for a marking. Measure it, or read the value from the reel label or the board's BOM.
What about capacitors?
Chip capacitors are almost never marked; the three-digit code on larger ones (104) works the same way in picofarads. The capacitor code calculator reads those.