Larger chip resistors carry a short code instead of a value. Three systems cover almost everything you will find on laptop and desktop boards, and this decoder recognises all of them. Type the code exactly as printed — the calculator works out which system it is.
How to use it
Type the marking: 103, 4R7, 1002, R010, 01C, or 000 for a zero-ohm link. Read the value, the system and the usual tolerance for that system. Rotate the board under the microscope if the code is ambiguous — 601 upside down reads 109.
The three marking systems
| System | Example | How to read it |
|---|---|---|
| 3-digit | 472 | Two digits, then the number of zeros: 47 × 10² = 4.7 kΩ |
| 4-digit | 4701 | Three digits, then the number of zeros: 470 × 10¹ = 4.7 kΩ |
| R notation | 4R7, R010 | R is the decimal point: 4.7 Ω, 0.010 Ω (10 mΩ) |
| EIA-96 | 01C | Two digits index the E96 table, the letter is a multiplier: 100 × 100 = 10 kΩ |
| Zero-ohm | 0, 000 | A link, not a resistor |
Three-digit codes usually mean 5 % parts from the E24 series; four-digit codes and EIA-96 codes mean 1 % parts. EIA-96 letters are 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) and F (×100,000).
Worked example: a current-sense resistor
Next to a charger IC sits a 1206 resistor marked R010. R marks the decimal point, so the value is 0.010 Ω — 10 mΩ, a typical current-sense value. A normal multimeter cannot measure it accurately, but the code tells you exactly what the replacement must be. The role of such resistors is explained in Current Sense Resistors in Laptop Charging Circuits.
When there is no marking
Resistors in 0402 and smaller packages usually carry no code at all. Take the value from the schematic, using the reference designator you find in the boardview. A measured value in circuit can be misleading because of parallel paths, as covered in How to Test a Resistor with a Multimeter (In and Out of Circuit). More marking systems — for capacitors, diodes and transistors — are in SMD Component Marking Codes: How to Identify Unknown Parts.
FAQ
What does 000 mean on a resistor?
It is a zero-ohm link used as a jumper or an option. It should measure close to 0 Ω.
Why does my decoded value not match the measurement?
In circuit, other parts in parallel lower the reading. Lift one end or compare with the schematic before deciding the resistor is faulty.
Is a 4-digit code more precise?
It indicates a tighter-tolerance part, usually 1 %, and allows a third significant digit.