The English Mastiff is typically considered the breed of dog that weighs the most. Adult male Mastiffs can weigh up to 220 pounds or more, while females can weigh up to 190 pounds or more. However, it is important to note that a dog's weight can depend on a number of factors, including its diet, exercise habits, and overall health. It is important for all dogs to maintain a healthy weight to help ensure their overall well-being and reduce the risk of obesity-related health problems.