Surface mount resistors come in a variety of sizes. The smallest size is the 0201 package which measures a tiny 0.6mm x 0.30mm. You can
find surface mount resistors as large as 6.3mm x 3.1mm which is referred to as size 2512.
Keep in mind that every manufacturer may have a variation of the measurements and power ratings other than what is in the chart below.
These numbers are just for reference. Actual parts may vary slightly in dimensions and ratings.