SMD Resistor Identification
Table of Contents
How The 3-code Resistor Value Works
Thankfully for makers, SMD resistors (even down to 0603 sizes), have a three number code printed on them that can be used to identify its resistance. However, this number doesn’t tell us the tolerance of that resistor, nor does it indicate its power, which can make it difficult to replace should a resistor break.
In most cases, the number code printed on a resistor is split up into two different numbers; the first two which indicate a decimal value, and a single number that indicates a multiplier. The multiplier is not the number of time the number is multiplied, but the number of times that number is multiplied by 10. The best way to see how this works is to go through a few simple examples.
The Code System
SMD Resistor Code Examples
Example 1 - Decoding 123
In this case, the first to numbers are 1 and 2, so the decimal value is 12. The third number is 3, meaning that we need to multiply the number by 10 three times. So, 12 becomes 12 x 10 x 10 x 10 which is 12,000, or 12K ohms.
Example 2 - Decoding 56
In this case, the first two numbers are 5 and 6, so the decimal value is 56. As there is no third number, we don’t multiply the number at all (being 0 lots of 10). So, the value of this resistor would be 56 ohms.
Example 3 - Decoding 225
In this case, the first two numbers are 2 and 2, so the decimal value is 22. The third number is 5, meaning that we multiple the number by 10 five times. As such, the value of this resistor would be 22 x 10 x 10 x 10 x 10 x 10 which is 2,200,000, or 2.2M ohms.