SMD Resistor Code Lookup
Three digits, four digits, or a cryptic two-digits-and-a-letter. Whatever is printed on the little black brick, type it in.
Three systems on one package
Three digits read like the classic resistor code: two digits and a zero count, so 472 is 4700 Ω. Four digits mean a 1% part: three digits and the zero count, so 4702 is 47 kΩ. And two digits plus a letter is EIA-96, where the digits index a table of values and the letter is the multiplier: 01C is 10 kΩ. This tool speaks all three.
When there's an R
An R is a decimal point. 4R7 is 4.7 Ω, R047 is 0.047 Ω, the kind of value you meet in current-sense resistors. And a plain 0? That's a zero-ohm resistor, a wire dressed up as a component so the pick-and-place machine can install it.
Why the codes changed
Three-digit codes ran out of room once 1% parts became normal. Two significant digits cannot express 4.53 kΩ, so the four-digit system added a third digit and the EIA-96 system went further: two digits index a 96-value lookup table and a letter carries the multiplier, which fits a 1% value onto an 0603 part with room to spare. That is why an 0805 might read 4701 while the 0603 beside it reads 22B and both are perfectly ordinary resistors.
Reading a part you cannot decode
Some chip resistors carry no marking at all. Below 0603 there is simply no space to print, so manufacturers leave them blank and expect the reel label to be the record. If the part is already on a board, measure it in circuit only as a rough check, because everything else on that node measures in parallel with it. Lift one end, or read the value off the schematic instead. A blank part that measures near zero is usually a zero-ohm link rather than a resistor with worn printing.