Marking on surface-mount resistors
Surface-mount (SMD) resistors in sizes such as 0805 or 1206 carry a short printed code instead of color bands. Three systems are common. The smallest sizes, 0402 and below, usually carry no marking at all.
3-digit code (usually ±5%)
The first two digits are significant figures, and the third is the power of ten:
- 472 = 47 × 10² = 4,700 Ω = 4.7 kΩ;
- 103 = 10 kΩ;
- 220 = 22 Ω (zero zeros added);
- 100 = 10 Ω, not 100 Ω.
4-digit code (usually ±1%)
Three significant figures and a multiplier:
- 4702 = 470 × 10² = 47 kΩ;
- 1001 = 1 kΩ;
- 2490 = 249 Ω.
The letter R
An R marks the decimal point for small values: 4R7 = 4.7 Ω, R10 = 0.1 Ω, 0R = zero-ohm jumper. The calculator handles numeric codes; read R codes directly.
EIA-96 code (±1%)
Small 1% resistors use two digits and a letter. The digits (01 to 96) give the position in the E96 series of standard values, and the letter gives the multiplier:
| Letter | Multiplier |
|---|---|
| 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 |
Examples: 01C = 100 × 100 = 10 kΩ; 68X = 499 × 0.1 = 49.9 Ω; 30A = 200 Ω.
The E96 values follow a geometric series: value number n is 100 × 10^((n − 1) ÷ 96), rounded to three digits, from 100 (01) to 976 (96).
Tips for reading SMD codes
- Make sure you read the part the right way up: 0R1 and 1R0, or 801 and 108, are easy to confuse.
- On boards with very small parts, check the schematic or measure with a multimeter; in-circuit readings can be off because of parallel paths.
- The same 3-digit system is used on SMD capacitors and trimmers, but in picofarads for capacitors.
- Some manufacturers use their own codes, especially for current-sense resistors. When in doubt, look up the datasheet.