Surface mount resistors, SMD resistors use surface mount technology, SMT to provide considerable advantages in terms of space saving and automated manufacture of printed circuit boards.

TYPICAL SMD RESISTOR POWER RATINGS

PACKAGE STYLE TYPICAL POWER RATING (W)
2512 0.50 (1/2)
2010 0.25 (1/4)
1210 0.25 (1/4)
1206 0.125 (1/8)
0805 0.1 (1/10)
0603 0.0625 (1/16)
0402 0.0625 – 0.031 (1/16 – 1/32)
0201 0.05

COMMON SURFACE MOUNT RESISTOR PACKAGE DETAILS
PACKAGE STYLE SIZE (MM) SIZE (INCHES)
2512 6.30 x 3.10 0.25 x 0.12
2010 5.00 x 2.60 0.20 x 0.10
1812 4.6 x 3.0 0.18 x 0.12
1210 3.20 x 2.60 0.12 x 0.10
1206 3.0 x 1.5 0.12 x 0.06
0805 2.0 x 1.3 0.08 x 0.05
0603 1.5 x 0.08 0.06 x 0.03
0402 1 x 0.5 0.04 x 0.02
0201 0.6 x 0.3 0.02 x 0.01

You’ve probably encountered this before — you have a circuit board that is poorly documented, and want to know the part number of a tiny SMD chip. Retro computer enthusiast [JohnK] recently tweeted about one such database that he recently found, entitled The Ultimate SMD Marking Codes Database. This data base is only a couple of years old judging from the Wayback Machine, but seems to be fairly exhaustive and can be found referenced in quite a few electronics forums.

The ultimate SMD marking codes database
https://smd.yooneed.one/