The Bullmastiff is a relatively large dog. The American Bullmastiff Association standard calls for dogs to be between 25" and 27" tall at the withers and between 110 lbs. and 130 lbs. though current judging trends often favor a dog slightly larger than this. Bitches are to be between 24" and 26" tall and 100 to 120 lbs. They make good parents, and often produce more than six puppies in a litter.