The largest dog breed in terms of height, measured at the shoulder, is the Great Dane. When it comes to mass, however, the English Mastiff is the biggest.
Great Danes can grow to average heights of 28 to 34 inches at the shoulder and weights between 100 to 200 pounds. English Mastiffs do not stand higher than 30 inches, but they can weigh up to 220 pounds.
The largest single dog in the world is Zeus, a Great Dane who weighs 150 pounds and measures 3-feet 8-inches in height. Although large dog breeds are often intimidating, most possess a mild temperament and are very friendly; traits that are highly desirable in a companion or family pet. Both breeds are loyal and have strong, protective instincts.