Per AKC breed standards, in regard to weight, expected Maltese size (as a full-grown adult dog) is under 7 lbs. (3.17 kg).
This means any weight from 6.9 lbs. (3.12 kg) and less.
This said, it is nearly impossible for an adult Maltese to be in the 1-pound range. It is also very rare for a Maltese to be in the 2-pound range. You may see this every now and again; however, it is the exception and not the rule.
Therefore, most Maltese will be 3 to 7 lbs. as adults.
However, the 'under 7 lb.' range is for dogs appearing in the show ring. And it is a guideline for breeders in regard to their goals, as they strive to produce pups that meet the strict AKC standards.
So, it is not unheard of for some Maltese to be 7, 8 or even 9 pounds.