SMD Resistor Code Calculator

An SMD chip resistor's top face is only a millimeter or two across, so instead of color bands it carries a few digits or letters. There are four common schemes, and you can tell them apart by the number of characters and whether a letter is present. The shared idea is simple: the leading digits are significant figures and the last digit is a power of ten (how many zeros to append).

3-digit: R = (d1 d2) × 10^d3
4-digit: R = (d1 d2 d3) × 10^d4
EIA-96:  R = E96[nn] × multiplier(letter)

Worked examples

• 103 → 10 × 10³ = 10,000 Ω = 10 kΩ — not 103 Ω.
• 1002 → 100 × 10² = 10 kΩ. The same value in 4-digit form usually signals a ±1% part.
• 4R7 → 4.7 Ω; R010 → 0.010 Ω = 10 mΩ (a current-sense shunt).
• 01C → first E96 value, 100, times C (×100) → 10 kΩ. 68X → 68th value, 499, times X (×0.1) → 49.9 Ω.
• 000 or 0 → a 0 Ω jumper, used to hop over traces or select options.

Whether a chip carries a marking at all depends mostly on its size. The table below lists common thick-film chip resistor sizes with typical power ratings at 70 °C ambient and the marking you are most likely to find. Ratings vary between manufacturers and product lines (high-power variants exist in every size), so always confirm against the datasheet.

Note that the marking tells you nothing about the resistor technology. A general-purpose thick-film part and a precision thin-film part (±0.1%, 25 ppm/K) can carry identical codes. If a board uses precision resistors in a reference divider or current-sense circuit, replacing them with ordinary parts of the same marked value will quietly degrade accuracy.

• Measure it out of circuit, or at least compare readings across several identical positions on the board; parallel paths make in-circuit readings low.
• Check that it really is a resistor: capacitors show no DC continuity, inductors and ferrite beads read close to 0 Ω, and resistors read a stable, finite value in both directions.
• Use context: a part next to a regulator's feedback pin is part of a divider, a large chip in series with the supply is often a current-sense shunt, and parts on I²C lines are usually pull-ups of 2.2–10 kΩ.
• Read the reel label or the manufacturer part number if you still have the packaging; it encodes value, tolerance, size and TCR.

A practical example: you find an 0805 chip marked '1001' beside a buck converter's feedback pin and a matching '3161' on the other side of the node. Decoding gives 1.00 kΩ and 3.16 kΩ, both E96 values, so these are ±1% feedback resistors and their ratio sets the output voltage — exactly what the voltage divider calculator can check for you.

• Reading 103 as 103 Ω: the last digit is always the number of zeros. This is the classic error.
• Reading the chip upside down: 601 and 109 swap when flipped. Use the silkscreen or neighbouring markings for orientation.
• Mistaking EIA-96 for a 3-digit code: two digits followed by a letter is EIA-96, so 01C is not '01 × 10^C'. Conversely, '47R' is normally 47 Ω in R notation, but some EIA-96 makers use R as an alias for Y (×0.01), so the tool shows both readings.
• Confusing it with a capacitor: ceramic capacitors can use '103' too, meaning 10 nF (in pF). Most chip capacitors carry no marking at all, though.
• 0402 and smaller: usually unmarked because there's no room. Check the reel label, the BOM, or measure.

When repairing a board or reviving a discontinued design, reading part values is step one. Always cross-check a decoded marking with a meter; in-circuit readings come out low because of parallel paths, so compare several identical parts before deciding. For new designs, put the value, tolerance, size and rating in the BOM — e.g. '10 kΩ ±1% 0603 (1608) 1/10 W' — rather than the marking. Imperial (0603) and metric (1608) size codes get mixed up constantly, so see our docs article on size codes. KEMI's SMT assembly quotes source parts from exactly this kind of BOM.