The best way to get a growth chart is to talk to the breeder you got your American Bulldog from. Different lines have very different growth rates. If you adopted your dog, check around with people who know the breed well.
It would depend on your dog's bloodline in order to be accurate, thus getting a growth chart from the breeder is the best avenue to take. Your breed of dog will normally gain 10 lbs a month for the first seven or eight months.
I'm sure if you contact the breeders association for American Bulldogs they will be able to provide you with some guidelines. Another option would be to try the local dog showing authorities.
