No group of animals in the world are as diverse as dogs. Dogs come in all shapes and sizes. Some are bred for different jobs and sports.
The smallest dog breed in the world is is the Chihuahua. Chichuahuas can weigh up to nine pounds and are usually no more than 9 inches tall.
The tallest dog breed in the world is the Irish Wolfhound and they can be 3 feet tall at the shoulders.
The heaviest breed of dog in the world is the English Mastiff with weights over 200 lbs. not uncommon.
There are so many different breeds of dogs that it is most likely you will not have even heard of some of them.
If you select a dog breed from the list the link will take you to the wikipedia website which has some fantastic information about each dog breed.