Dogs that weigh 20 lbs and less are generally considered small, though they're nearly in the territory of medium dog breeds. All dogs on this list usually range from 3 lbs to 18 lbs, from pups to full-grown canines. Medium dogs usually have three subdivisions: medium-small, medium, and medium-large. Collectively, however, they weigh between 20 and 60 lbs. For apartments, medium-sized dogs are a good choice, too. Large dog breeds, however, weigh more than 70 pounds. Though all the dog breeds we've listed above categorize as small dogs, some might grow slightly bigger than expected if they tend to gain extra weight.