How Long Does it Take for a Puppy to Get to Its Full Size?

While most pups are considered adults when they reach 1 year old, the fact is, dog breeds mature at slightly different rates, and not all dogs are full-grown on their first birthday. Small breeds reach adult size more quickly; some larger breeds may not be fully grown until around 2 years of age. Until they are fully mature, pups need special nutrition to encourage healthy growth at an appropriate rate.

A puppy reaches what is considered to be his adolescence between the ages of 6 months and 18 months, depending on the breed. During this approximately six-month transitional period between puppyhood and adulthood, Fido is almost at the size he will be as an adult, with just a bit of growing left for his body to do. If you haven't spayed or neutered your pup, little Fido will become sexually mature during his adolescence and capable of reproducing. His entire soft puppy coat will shed and his adult coat will grow in. At the end of his adolescence, Fido officially becomes a fully grown adult.

After adolescence, your pooch should be at his full adult height. Once your pup's bones stop growing, he won't get any taller, although he may still put on some weight and muscle during the couple of months after his skeleton stops developing. Small breed dogs, those that weigh no more than 30 pounds as healthy adults, stop growing at 10 months; by 12 months, they reach their full adult size. Medium breeds, those weighing up to 80 pounds as adults, may reach their adult size between 12 and 16 months of age, according to the Cesar's Way website. Large and giant breeds, those over 80 pounds, may reach their full size between 18 months and 2 years old.

If your puppy is still a youngling but you want to get an idea of what size he'll be as an adult, you can estimate his adult weight by doubling his weight at 4 months old, recommends PetEducation.com. For giant breeds, double your pup's weight at 5 months old, instead, to estimate his adult weight. You can also look to your pup's parents, if you know who they are, to get an idea of what his full adult size will be. A less exact way of predicting a dog's size is to look at his paws; large breeds tend to have large paws as young pups that they eventually grow into as adults, according to the VetStreet website.

It's important to feed your growing pup according to his breed and age. Puppy food contains more calories and nutrients like protein, fat, calcium and phosphorus to encourage and support healthy growth. Large and giant dog breeds, though, need a special food designed specially for them. Puppy foods for large breeds contain fewer calories and less phosphorus and calcium to encourage slower bone growth. These formulas don't encourage rapid growth as typical puppy formulas do, preventing orthopedic and joint diseases later in life. Feed any breed of dog a puppy formula appropriate for his breed until he reaches at least 80 percent of his adult size, usually around 1 year old. If you're unsure, consult with your vet to get her feeding recommendations for your particular pooch.