How tall were the earliest ancestral horses?

The earliest ancestral horses, known as Hyracotherium (commonly referred to as Eohippus or the "dawn horse"), were diminutive animals that lived during the early Eocene Epoch.12

Depending on the specific species, these early mammals stood approximately 30 to 60 cm (1 to 2 feet) high at the shoulder. Other measurements indicate they stood about 4.2 to 5 hands high, which is equivalent to roughly 42.7 to 50.8 cm (16.8 to 20 inches). Some of these forest-dwelling, browsing animals were described as being no larger than a terrier.123