World Largest Breed Dog

The largest dog in terms of mass is an English Mastiff by the name of Zorba.  He weighed in at 343 pounds and measured almost 8 feet from tail to nose.

Here is the list of the largest breeds:
Irish Wolfhound: weight: 105-125 lbs. height: 35-35 in.
Great Danes: weight: 100-120 lbs. height: 28-32 in.
English Mastiff: weight: 175-250 lbs. height: 27.5-32 in.
Neopolitan Mastiff: weight: 150-180 lbs. height: 26-31 in.
Newfoundland: weight: 130-150 lbs. height 28-30 in.
Saint Bernard: weight: 150-200 lbs. height: 27-30 in.