Mastiffs are amongst the fastest growing breeds, reaching 200+ lbs from just 10-15 lbs as puppies.
Great Dane puppies weigh just 5-10 lbs but rapidly grow into 150+ lb gentle giants.
St Bernard puppies weigh 20-25 lbs but grow to 150-200+ lbs as adult dog.
The Newfoundland grows from a 25 lb pup into a 100+ lb dog known for its lifesaving abilities.
Irish Wolfhounds start as 35 lb pups then grow to imposing 130-180 lb height.
Most largest growing dogs share traits like large bones, rapid growth plates, and genetic potential to grow.
Ensure proper nutrition to support healthy bone growth for puppies growing the most.