The estimated weight of a puppy depends on its heredity, breed, health and nutrition, and also on the size of breed, whether toy, small, medium, large or giant breed. For toy and small breeds, multiply their weight at 6 weeks by four to get a rough idea of their estimated adult weight; for medium and large breeds, double their weight at 14 weeks, and add half of their original weight to it.
Generally, a puppy's birth weight doubles in a week, and it increases consistently by 5 to 10 percent every day for six weeks. After that, you can expect a weekly gain of 5 ounces for a small breed pup, or 2.5 pounds for a large breed pup. Small and medium breeds reach maturity in less than a year, while large and giant breeds take a longer time, sometimes two or three years, to reach their full growth potential.
If your puppy is a mixed breed, take a look at your puppy's parents. Its adult size will be between the sizes of both the parents. If you don't have any information about the parents, you can either take the opinion of your veterinarian or breeder, or you can get the puppy's DNA tested. This informs you about the dominant breeds in your puppy's ancestry.
Underfeeding affects the growth and development of the puppy. Furthermore, overfeeding, or giving unnecessary supplements, makes the puppy obese and puts it at risk of lifelong muscle, bone and joint problems. Both do not let the puppy reach its full potential.