This brief summary may assist when identifying surface mount resistors. However, keep in mind this is a generic overview and may differ based on manufacturer or specific resistor series.
SMD resistor sizes 0201, most 0402, and some 0603 are not marked due to their small physical size. Resistance verification on these will have to be done by an actual measurement.
For lower ohm resistors with markings, it is common to see an “R” or an Ohm symbol used for the decimal place. Below are a couple examples of this:
0.22 Ohm (220mOhm):
0.02 Ohm (20mOhm):
-If the multiplier (last digit) is a zero, this also means a decimal:
24 Ohm:
For higher ohm resistors with markings it is common to see a multiplier with digits 1-9 representing the number of zeros:
2 Multiplier Example:
10,000 Ohm (10kOhm)
3 Multiplier Example:
10,000 Ohm (10kOhm)
The letter K or M may also be used for higher ohm resistors. K meaning kilo or a multiplier of 3, M meaning mega or a multiplier of 6 as shown below:
Special Markings
Special markings such as a bar are typically manufacturer/series specific such as the RT series from Yageo datasheet.
Red ink is commonly used to indicate that a resistor has a higher precision or tighter tolerance, such as ±1% or smaller for applications where precise resistance values are critical, but always refer to the manufacturer’s documentation for precise details since the exact meaning can vary between manufacturers.
There is another marking method known as the EIA - 96 MARKING RULE, in which the part marking values are based from a table similar to below.
The the first two-digit “Code” represents the “Value”, and the “Letter” represents the multiplier, or number of zeros to add or subtract.
For example, AC0603FR-071K21L is marked “09B”
- “09” Code calls out 121 (Ohms) Value
- “B” calls out the multiplier 1x10
Therefore, marking code “09B” calls out a resistance value of 1210 Ohm, or 1.21kOhm.
There are sometimes slight table variations between manufacturers, but will result in the same value regardless, below table is a variation example:
See also:
https://forum.digikey.com/t/yageo-mfr-resistor-size-difference/20390
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Yageo Resistor Part Numbering RC_L Series
Yageo MMF Resistor Part Number Breakdown
Identify Yageo AC0603FR-071K21L Chip Resistor Marking