What is the difference between a horse and a pony? The primary distinguishing factor of a horse from a pony is the animal's height. A mature pony will always measure less than 14 hands and two inches at the withers (a hand equals four inches) and a mature horse measures over 14.2. The difference between horses and pony can be a bit more complicated, however, as some short "pony breeds" such as Icelandics, are correctly referred to as horses, while in breeds like Morgans and Arabians, even a horse under 14.2 is considered a "horse". These breed differences are an exception to the rule, however, and generally the 14.2 rule applies to outline the difference between a horse and a pony.