Working with horses is a pleasure and a challenge. There are many things to learn; sometimes you almost despair of every knowing it all. One thing is the common use of terms not really used anywhere else. For example, a horse's height is measure in "hands."
Start by understanding what a "hand" is. A "hand" is four inches. So when a horse is ten hands high, he is forty inches from the ground to the top of his withers.
Purchase or borrow a measuring stick. These will measure exactly how tall your horse is in "hands." This is the easiest method.
Make sure you are measuring from the spot where the horse's hoof touches the ground to the very top of his withers.
If you cannot locate a horse measuring stick, you may use a measuring tape. Take the total number of inches and divide by four. This will give you the number of hands.
Do not round up. Be exact. If a horse is sixty-three inches high, he is 15.3 hands tall. in other words, 15 hands and 3 inches.