There is no official standard that defines a teacup Pomeranian. Pomeranian dogs are toy dogs and normally weigh between 3 and 7 pounds at maturity.
Pomeranians were originally bred down to toy size from a larger dog native to Pomerania, a region that straddles the border between Germany and Poland. The original breed weighed about 30 pounds. Reputable breeders do not try to produce dogs that weigh less than 3 pounds, as these dogs do not meet American Kennel Club standards and are too small to be bred safely. Because the Pomeranian has already been bred down to as small a size as its ancestry permits, dogs advertised as teacup Pomeranians are often mixed breeds rather than pure Pomeranians.