The largest dog ever depends if you’re looking at the tallest, longest or heaviest. Freddy the Great Dane in England measured 40.75 inches tall, while the Old English Mastiff Aicama Zorba in England measured 8 feet, 3 inches from nose to tail and was also the heaviest dog in the world at 343lbs. Great Danes are the tallest dog breed and English Mastiffs are the heaviest.