SMD Resistor Code Calculator (3-Digit, 4-Digit & EIA-96)
Convert the numeric marking printed on a surface-mount (SMD) chip resistor into a resistance value. Supports 3-digit codes, 4-digit codes (precision resistors), and EIA-96 codes (2 digits plus a letter), with the format auto-detected from your input.
What Is an SMD Resistor Code?
A surface-mount (SMD) chip resistor is a tiny component that gets soldered directly onto a circuit board, and its body is far too small to carry the printed color bands used on a leaded resistor. Instead, the industry standardized short marking codes made up of digits (and sometimes a letter) to communicate the resistance value and, in some cases, the tolerance. This tool converts that printed code into an actual resistance value expressed in ohms (Ω), kilohms (kΩ), or megohms (MΩ).
It supports three separate marking schemes: the "3-digit code," the "4-digit code" used on precision resistors, and the "EIA-96 code," which pairs a two-digit number with a trailing letter. You can let the tool auto-detect which scheme is in play based on the length and character makeup of what you type, or you can select the scheme yourself if you already know it. It's especially handy when you're looking at a component on a populated board and need to work out its resistance on the spot.
How to Look Up an SMD Resistor Code
- Choose the code format The scheme depends on whether the printing is all digits or ends in a letter. If you're not sure, leaving the format on "Auto-detect" works fine for most cases.
- Enter the marking exactly as printed Using a loupe or a stereo microscope, read the digits and letter on the resistor body and type them into the input field in the same order they appear. Letter case doesn't matter.
- Check the calculated result As soon as you type, the tool displays the resistance value and the format it detected. It also shows the significant-figure-times-multiplier breakdown, so you can use it to double-check your own mental math.
- Confirm with a multimeter if anything looks off If you suspect the printing is worn or you may have misread a character, measure the resistor directly with a multimeter and compare that reading against the tool's result.
Tips for getting more out of it
- 3-digit codes are common on general-purpose SMD resistors (typically ±5% tolerance), while 4-digit codes tend to appear on precision resistors rated ±1% or tighter. The digit count alone gives you a rough sense of precision.
- An EIA-96 code packs one extra significant digit (three digits of precision) into just two numeric characters, letting even tiny chip resistors carry a high-precision printed value.
- "Auto-detect" guesses the format from the length and character types of your input (digits only vs. ending in a letter). If the guess doesn't match what you intended, pick the format explicitly from the dropdown.
- A 0Ω jumper resistor is usually marked "000" or "0" rather than a real resistance code — while "000" can technically be parsed as a 3-digit code, it's really a special marking meaning "connect this trace directly."
- When reading a code under a loupe or microscope, worn printing can make similar characters like 0/D or 1/I hard to tell apart — checking from a couple of angles helps avoid misreads.
Where This Tool Comes in Handy
Identifying parts during board repair and fault diagnosis
When you're trying to work out the role a resistor plays on a failed board, the first step is usually reading its marking code to get the resistance value, then cross-checking that figure against the schematic or a known-good board.
Sorting salvaged parts for electronics hobby projects
When reclaiming chip resistors desoldered from a junk board for reuse, you can convert each faint, hard-to-read code one at a time and organize your salvaged parts bin by actual resistance value.
Verifying components during sourcing and BOM creation
Before committing a part to a bill of materials, you can sanity-check that a purchased lot of chip resistors actually matches the specified value by decoding the marking on a sample unit.
Learning the EIA-96 scheme if it's unfamiliar
Unlike 3-digit and 4-digit codes, an EIA-96 code can't be read at a glance from the digits alone. Working through real examples with this tool is a good way to internalize how the lookup-table-based encoding actually works.
Glossary
- SMD (Surface-Mount Device)
- A component designed to be soldered directly onto the surface of a circuit board rather than inserted through drilled holes. Chip resistors and chip capacitors are common examples.
- 3-digit code
- A marking scheme in which the first two digits are the significant figures and the third digit is a power-of-ten multiplier. For example, "103" means 10 × 10³ = 10,000 Ω (10 kΩ).
- 4-digit code
- A marking scheme in which the first three digits are the significant figures and the fourth digit is the power-of-ten multiplier. Because it carries one more digit of precision than the 3-digit code, it's commonly used on precision resistors rated at ±1% tolerance or tighter.
- EIA-96 code
- A marking scheme defined by the Electronic Industries Alliance (EIA) in which a two-digit number (01–96) is looked up in a standardized table to yield three significant figures, and a trailing letter encodes the multiplier. It packs high precision into very few printed characters.
- Multiplier letter code
- The single letter (Z, Y, X, A, B, C, D, E, or F) appended to an EIA-96 code, which represents the power-of-ten multiplier — ranging from ×0.001 to ×100,000 — applied to the significant figures.
- Tolerance
- The percentage by which a resistor's actual resistance is allowed to deviate from its stated value. On leaded resistors this is shown as a color band, but on SMD resistors it's typically tracked separately through the part number or datasheet rather than printed on the body itself.
- Significant figures
- The digits within a marking code that represent the actual numeric value of the resistance, before the multiplier is applied — the first two digits in a 3-digit code, or the first three digits in a 4-digit code.
- Jumper (zero-ohm resistor)
- A chip component with a resistance of 0 Ω that functions as a wire bridge across a trace on the board rather than as a true resistor. It's often marked "000" or "0," which serves a different purpose than an ordinary resistance code.
Frequently Asked Questions
Side Note — Ever-Shrinking Resistors and Their Marking Tricks
As electronic components have gotten smaller and smaller, resistors have moved to surface-mount (SMD) packaging at an accelerating pace. The colored bands used on a traditional leaded resistor simply won't fit on the surface of a chip just a few millimeters across, which is why short marking codes made of digits (and occasionally letters) were introduced instead.
The 3-digit and 4-digit codes are essentially the color-code idea translated straight into numbers, but the EIA-96 code takes things a step further. By preparing a standardized lookup table in advance, two numeric digits alone can express 96 possible significant-figure values (effectively three digits of precision), with the numeric part acting purely as an "index" into that table. This saves printing space while matching the precision of a 4-digit code.
In recent years, even tinier packages such as 0402 (0.4 mm × 0.2 mm) and 0201 chip resistors have become common, and an increasing number of these parts skip printing altogether (unmarked resistors). In that case you have to identify the resistance from the tape-and-reel label or reel part number instead, so visual identification via a marking code is likely to remain limited to parts above a certain size going forward.