Going strictly by height, according to Guinness World Records (GWR) that would be the great Dane. This sleek, long-legged breed has held the height record for tallest dog for more than two decades.
The tallest dog ever in GWR history was a great Dane called Zeus who stood 3 feet, 8 inches (1.1 meters) tall from the ground to the withers (the ridge between the shoulders of his front legs). Zeus lived in the U.S. and died in 2014.
The current recordholder for tallest living dog is another great Dane named Freddy who lives in Essex, England. When he was measured for GWR in 2016, Freddy stood 3 feet, 4 inches (1.1 meters) from ground to withers, but when he stands on his hind legs (not an official GWR measurement), he's more than 7 feet (2.3 meters) tall!
Freddy is a great example of not judging a book by its cover. His owner, Claire Stoneman, told The Telegraph he was the "runt of the litter" when he was a puppy. (That's Freddy pictured on the right in Stoneman's tweet below.)
Speaking of official measurements, GWR measurements are all performed by a professional veterinarian. To be eligible for a GWR, dogs must be at least 1 year old and possess a vet-certified "clean bill of health." But the famed records-keeper no longer accepts claims for heaviest or lightest pets.
In an email, Amanda Marcus, public relations manager with Guinness World Records North America, Inc., explained why. "We appreciate that the welfare of the pet would be, in the majority of cases, at the forefront of the owner's mind," she says. "We had, however, become increasingly concerned that owners would potentially be encouraged to over or underfeed their pets in the quest for recognition. Therefore, to avoid any undue suffering to any animal, we have ended our interest in such records."