Every dog is different, and not every dog is pure-bred – so the answer to this question will vary, depending on who you ask. Some small-breed dogs will be larger than others, and some of the smallest can be considered Toy breeds. However, the most commonly accepted definition of a small breed is any dog that:
Scientifically, smaller mammals have a greater surface area to volume ratio – they lose body heat faster and therefore they burn energy more rapidly than larger dogs. In other words, the metabolic rate of a Chihuahua, Maltese, Shih Tzu, Corgi, Pug, or Pom is higher than it is in a big dog such as a Doberman, German Shepherd, Goldendoodle, or Mastiff. If they don’t eat frequently enough, they can use up the energy in their systems and become hypoglycemic!