Puppies start out as tiny creatures and grow quickly in the first few months of life. Many dog owners try to estimate how much their puppy will weigh as an adult, but due to differences in breeds and growth rates, an exact number is not possible. A simple formula can give an estimate of your dog's weight at one year of age; however, you must weigh your dog after its initial growth period for a more accurate weight estimate.

Weigh your puppy at the end of its initial growth spurt. For small dogs, the growth spurt usually slows at 12 weeks. For medium dogs, weigh at 16 weeks, and for large dogs, at 20 weeks.

Divide your puppy's weight from Step 1 by its age in weeks at the time of the weighing. For example, if your beagle is 16 weeks old and weighs 5.44kg., divide 12 by 16, yielding 0.75. This number is your puppy's rate of growth in pounds per week. So, your beagle's growth rate is 0.34kg. per week.

Multiply your puppy's weight of growth from Step 2 by 52, which is the number of weeks in a year. A growth rate of 34kg. per week times 52 weeks equals 17.7kg. This number is the estimate of your dog's weight at one year old, when most dogs stop growing and are considered adults.