Mastiff puppies will grow to be quite large and will weigh between 130 to 220 lbs. by the time that they are full grown. As puppies, the dogs will weigh much less, but the exact weight varies depending on the dog's genetics and gender.
Most of the time the males weigh more than the females and it is not uncommon for male mastiffs to weigh more than 200 lbs. In 1989, the Guinness Book of Records recognized Zorba the mastiff as the world's largest dog at 343 lbs. Despite the mastiffs massive size, the dogs rarely bark and are quiet in the home. They also tend to be non-aggressive and undemanding making them good pets for individuals and families.