As a breeder, I am often asked, What is the average weight for a Mastiff Puppy/Dog? My answer is that it depends on a couple of factorsthe sex of the puppy, the overall bone size of a puppy, and the overall condition of the puppy. In our breed, Mastiffs do often have a size difference between the males and females. Males do tend to be bigger, have larger heads, and have larger bone. Thus, as a general rule, on the average a male is going to weigh more than a female.