Surface-mount resistors are too small for color bands, so they carry a short code instead. Type the code you see, such as 103, 4R7, 1002 or 01C, and you get the resistance and the marking system it uses.
It works backwards too: type a value and see how it's marked in each system, handy when you're hunting for a replacement on a board.
How to use
- Type the code exactly as printed, letters included. Upper or lower case both work.
- Read the value and the code type. 3-digit codes are usually ±5%; 4-digit and EIA-96 codes are ±1%.
- To find the code for a value, type it in the second box, for example 10k or 4.7.
- If the code isn't recognized, try reading it upside down: on a tiny part, 601 and 109 look alike.
How to read 3 and 4-digit SMD codes
The last digit is the number of zeros and the digits before it are the value. 103 is 10 followed by 3 zeros: 10,000 Ω, or 10 kΩ. 4702 is 470 followed by 2 zeros: 47 kΩ. The letter R marks the decimal point: 4R7 is 4.7 Ω and R10 is 0.1 Ω.
EIA-96 codes (1% resistors)
Small 1% resistors (0603 and smaller) use two digits and a letter. The digits are a position in the E96 table (01 = 100, 02 = 102 … 96 = 976) and the letter is the 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 and F ×100,000. So 01C is 100 × 100 = 10 kΩ.
Zero-ohm and unmarked resistors
A part marked 0, 000 or 0000 is a zero-ohm resistor, used as a jumper. Unmarked parts are common in 0402 and smaller; the only way to know their value is to measure them.