Guiness Book Record Breakers Boomer from North Dakota is now the world's biggest dog.Boomer, a 180-pound Landseer Newfoundland dog, stands with owner Caryn Weber at her home south of Casselton, N.D. The dog measures seven feet from nose to tail and stands 36 inches tall at the shoulders. Weber will send his measurements to Guinness World Records for consideration as the tallest living dog.