# How to find SMD resistor values and size?

I want to do reverse engineering of a PCB, in which some SMD resistors are used. On top of each resistor it has marked with 1R0, 150 , 0 etc. Is that represents the value of the resistor? If so, how to find the size of the resistor.

Say, a 2512 resistor SMD package has a width of 3.2mm and a length of 6.4mm, will it be available with all resistor values like 1kohm , 2kohm etc.

• Go to your favourite on-line component store and check. – Andy aka Jul 6 '17 at 12:24
• The number on the resistor is its value. Those appear to be 0805 sized parts. – JRE Jul 6 '17 at 12:28
• I feel like this has been asked 1000x times. There's no way this isn't documented. – Bort Jul 6 '17 at 17:35

The size of a SMD resistor affects it's thermal dissipation, and maximum voltage rating (although other factor are also likely to be limiting for most values in a range). Different types will also have different tolerance and temperature performance.

There is no significant interaction between the available resistance values, and the package size.

Yes. Or, to be more precise and exceed the minimum required character count for a cheap answer - Yes.

The number on the resistor is the value. It is gennerally in a form of $ABC$, where this means $AB \cdot 10^C$. For example, 100 would be 10 Ohm, 473 would be 47kOhm.

As others have said, different sizes give you different power and voltage ratings. However, other factors also influence this, such as the construction of the resistor (thick/thin film, wirewound, ...), as well as the PCB and mounting (sometimes you can get higher ratings of power by having thicker copper pads).

• I think you mean A*10^B, or maybe Aa*10^B..... AB*10^Clooks to me like two numbers, multiplied, then multiplied by 10^C. – Bort Jul 6 '17 at 17:41
• I don't know how else to word it, since it's usually three digits, AB being the first two, C the last. I would worry that if I say "AB" it would apear like it's two digits, or at least, there would be uncertanty which one of the two is two digits. – Joren Vaes Jul 6 '17 at 18:02
• @Joren (10A+B)*10^C – Matt Jul 6 '17 at 19:26