The Thinking Horse: Cognition and Perception
http://www.equineresearch.org/support-files/hanggi-thinkinghorse.pdf
How to Measure a Horse
The height of a horse is measured from the ground, to the highest point on the withers (the ridge between the horse’s shoulder blades). Although this measurement may be expressed in centimeters, it is more commonly expressed as “hands”, which are four-inch increments. For example, a horse that measures 60” from the ground to the withers is 15 hands tall, or 15 hh.