While there isn't a scientific formula to calculate your little pup's adult weight, you can use several factors to estimate it. Purebred pups likely will be around the same size as their parents, meaning that calculating their adult weight is pretty simple. If your pooch is a mixed breed, it might be a little more complicated to determine his adult weight.
How Much is That Doggie in the Window?
Puppies aren't fully grown until they're about 1 year old, although larger breeds don't stop growing until they're around 2 years old. Generally, you can double the weight of any 4- to 5-month-old puppy to estimate his adult weight, especially if you’re dealing with a large- to giant-breed of dog, according to PetEducation.com. Try to determine your pup's breed size based on the sizes of his parents or his general appearance. Multiply a toy- to small-breed pup's weight at 6 weeks of age by four to estimate his adult weight or a medium- to large-breed pup's weight at 14 weeks by 2.5, recommends Leo's Pet Care Veterinary Clinic website.
Other Factors to Consider
Some signs that your young mixed-breed pooch will grow into a large-breed adult include big paws and loose skin. Of course, overfeeding or underfeeding your dog can affect his eventual adult size and weight as well. Note that even if you know the size of your pup's parents, some pups are just genetic anomalies and may grow much larger or smaller than expected, according to Dogster. Mixed breed pups especially may surprise you with their eventual size because of their diverse lineage.