Any list of the worlds largest dog breeds can be disputed, especially if you look at individual specimens.  Just like humans, a dog can be fed a large amount and get heavy.  In fact, the Guinness Book Of Records no longer accepts records for the heaviest dog.  Even under normal circumstances, there are variations in a breed.  While the size of a Chihuahua is never going to beat the size of a Great Dane, dog breeds that are close to each other in size can certainly have one individual beat another.  Here are my candidates for the top five worlds largest dog breeds.

Top 5 - Worlds Largest Dog - Saint BernardCredit: http://en.wikipedia.org/wiki/File:Stbernardinsnow.jpg

 Number #1 – Saint Bernard

 Thought to descend from the Molosser, the Saint Bernard is a large dog famous for rescues in the mountains.  The Molosser includes several breeds of dogs, used as shepherd dogs in ancient Greece.  Is is thought that the Saint Bernard is descended from some of the dogs that traveled with Hannibal across the Alps during the Punic Wars. 

The average weight of these dogs is 140-264 pounds, and average height of 27-35 inches at the shoulders. 

 Today’s dogs look different than they did several hundred years ago, because they were threatened with extinction in the early 1800s, and so were cross bred with Newfoundlands to save the breed.  Although this breed is known for their rescues in heavy weather, this cross breeding limited their usefulness for this as it lengthened their fur.

Credit - http://en.wikipedia.org/wiki/File:Stbernardinsnow.jpg

Number #2 – English MastiffTop 5 - Worlds Largest Dog - English MastiffCredit: PD - http://en.wikipedia.org/wiki/File:Lukey%27s_Governor_(Mastiff).jpg

These dogs descend from dogs that the Romans used in their blood sports involving bears, bulls, and lions, as well as dog fighting.  In fact, it is thought that their origins go back even further, and that they were originally from Britain and brought to the Romans by the Phoenicians in the 6th Century BC. 

 Although not as tall as some other breeds, the English Mastiff is more massive and square of body.  It is the largest dog in mass.  The Standard height for this breed is 30 inches for the males and 150-250 pounds.

Before the Guinness World Records stopped the heaviest dog category, the record was held by Zorba, and he was 35 inches tall and weighed in 343 pounds.

 Number #3 – Neapolitan Mastiff

Standing 26-31 inches at the withers, and 130-155 pounds, the Neapolitan MastiffTop 5 - Worlds Largest Dog - Neapolitan MastiffCredit: PD - http://en.wikipedia.org/wiki/File:10_yr_old_Mastiff.JPG makes number three on the list.  This breed can be aggressive towards strangers, and it is a very protective type.  They are not good for the first time dog owner, as they need positive training and socializing training throughout their life.  The Neapolitan Mastiff is not a kid friendly dog, as it’s size can make it clumsy around children, and the socializing problems can be hard to deal with if the child has friends. 

Probably descended from the Molossus also, the breed has been around so long that it roots are lost.  The breed almost disappeared after World War II, but Piero Scanziani, and Italian painter, started a program to formalize the breed.

 Number #4 – Newfoundland

Bred in Newfoundland to be a working dog for fisherman, these dogs are known for their size,Top 5 - Worlds Largest Dog - NewfoundlandCredit: http://en.wikipedia.org/wiki/File:Newfoundland_dog_Smoky.jpg strength and calm disposition.  Growing to be 22-28 inches at the shoulder they usually weigh 130-150 pounds.  Some of these regularly weigh over 200 pounds with the largest recorded at 260 pounds. 

The breed started with dogs indigenous to the island, but probably gained some characteristics of the mastiffs when Portuguese fisherman and their dogs interacted with them in the 16th century.  Fanciful speculation is that the breed is descended from black bear dogs brought over by the Vikings around the 11th century, but there is absolutely no proof of this.

Credits - http://en.wikipedia.org/wiki/File:Newfoundland_dog_Smoky.jpg

 Number #5 – Great Dane

The origin of the Great Dane is unknown.  Some say it came from Germany, and is a cross between an English Mastiff and the Irish Wolfhound, and others say it originated in Denmark.  The name “Great Dane” first appears in 1749.  The minimum requirements that the American Kennel Club gives for a male of this breed is 30 inches tall at the shoulders and 120 pounds. Top 5 - Worlds Largest Dog - Great DaneCredit: http://en.wikipedia.org/wiki/File:Dogge_Odin.jpg

According to Guinness World Records, a Great Dane is the record holder for tallest dog living and tallest dog ever.  That specimen, Great George, tops out at 43 inches and is from Arizona in the United States.

 Summary

 These five, and probably several others, all come into the same weight range and can grow to be the worlds largest dog.  As breeds, the five listed here are my five largest.

Credit - http://en.wikipedia.org/wiki/File:Dogge_Odin.jpg