The breed of mastiff that is the largest is the English Mastiff dog breed.
The female English Mastiff weighs between 120 lbs to 170 lbs and the male English Mastiff weighs between 160 lbs to 230 lbs.
The English Mastiff is a very big dog and requires a lot of room to run around and requires a lot of food too.
You could spend $100.00 or more per month just on dog food for the English Mastiff so be prepared to spend money but the English Mastiff is a great dog.
They are also pretty protective and will bark when needed but they don't bark as much as other dogs do.