Puppies can become very large adult dogs. It is easy to fall in love with a cute, cuddly puppy, but you may not be prepared for what the dog will grow into. This is especially true for mixed breed puppies. Estimating your dog's adult size will help you prepare your home and determine if your dog will thrive in the environment you can provide. These methods can only provide an estimate. Your dog may be slightly larger or smaller than predicted.
Determine the breed or breeds that make up your puppy. You should know if your puppy is a purebred when you get it. Mixed breeds can be a bit more difficult to determine. Try to find out what breeds its parents were. You can ask your vet to help you determine the mix if you don't have information about the puppy's parents.
Look up the average size of your dog's breed. The American Kennel Club maintains a database of most breeds and includes weight and height ranges. It is common for females to be slightly smaller than males of the same breed. Mixed breeds with parents that are not similar in size may take after either the mother or father, and it can not usually be determined which parent the puppy will more resemble until it gets older.
Divide your puppy's current weight by its age in weeks to figure out its average growth per week. Then multiply this number by 52 to get the estimated adult size. This method is not always accurate, but gives a general idea.
Decide which size group your puppy fits into: small, medium or large. You will probably need your vet's help for a mixed breed dog. Find the estimated weight of small breed dogs by multiplying their weight at 6 weeks of age by 4. Medium size dogs should be measured at 14 weeks and multiplied by 2.5, and large dogs can be estimated to be half their size at 6 months of age. You can also use puppy weight charts. Simply find your dog's weight on the chart that corresponds to its age. Use the line that is closest to this value to estimate your dog's adult size.