Puppies of different sizes and breeds grow at different rates, some more quickly than others. Most dogs reach adult height at 1 year of age, large and giant breeds may take twice as long to reach their full height.
A puppy grows most rapidly during his first 6 months, after which growth continues at a slower pace as he begins to mature into an adult. By the time he reaches around 9 months old, a toy or small breed puppy will likely be at his full adult height, according to "Your Puppy, Your Dog: A Kid's Guide to Raising a Happy, Healthy Dog." Medium-size breeds usually reach their full height at around 1 year old. Large and giant breeds grow much more slowly; they won't reach full size until between 18 months and 2 years of age.
Adjusting to Growth
Because many pups are still growing until they reach 2 years, the Dogster website recommends purchasing adjustable collars, harnesses, crates and coats that will grow along with your pooch so you're not constantly purchasing and replacing size-appropriate items as he matures. Even after Fido reaches his full height, he may still continue to gain weight for up to an additional year during his adolescence, according to the Akolade Dobermans website.