The age at which a dog is fully grown depends on its breed size and can range from 6 to 24 months. Small breeds typically stop growing by the time they reach 6 to 8 months of age, while medium breeds might take just a bit longer to grow, reaching their adult size at around 12 months of age. Larger breeds take longer to reach full adult size than smaller breeds, with giant breed puppies growing until they are 12 to 18 months old, and very large pups like mastiffs may even reach their fully grown size at 24 months of age. However, its important to note that while all puppies are officially considered adult dogs once they reach one year old, puppies continue to grow in height and size while their bones are still developing.

Pet parents can estimate when their dog is fully grown by looking at their teeth. By six months, canine teeth should have fully erupted, and when the dog is around one, all 42 of the adult teeth should be fully erupted and in good condition. Another way to determine if a dog is fully grown is to have a veterinarian perform x-rays of the dogs long bones to observe if the growth plates are fully closed or not. If theyre closed, the dog is done growing.