You can get a rough idea of your puppy’s eventual adult height and weight by doubling the puppy’s height and weight at 13 weeks of age. Also knowing the weight of your puppy’s parents can give you an idea too. There normally are no guarantees on how much your puppy will weigh when he/she is an adult. Some breeder’s might put a guarantee for weight on their contract, but seldom do you find such a guarantee. Genetics is almost impossible to determine.