"Horses are measured in hands.....etc" Not on the continent nor at an international level they are not. Horse height is fully metric. One giant leap from hands to cm and meters.

Generally speaking for an adult anything under 1.62m is considered small unless the adult is particularly small then 1.52m might do if they are also light and or if the horse is a weight carrier. The average size for adults is any-thing from 1.62-1.72m for junior riders usually around 1.52-1.62 for kids anything under 1.42 m.