To accurately answer the question of how fast a horse can run requires a definition of the word run. Just as people run in different gaits, so does a horse, only more so. At a full-out gallop, an average horse can run from 15 miles an hour to over 30 miles an hour. If anything may be said for a horse, it is that there is no such thing as average.
In addition to determining what gait a given horse is using when it runs, you need to know what breed of horse he is, the condition of his health, and how he is fed, to know how fast he may be able to run.
Horses typically have four gaits at which they travel: Walk, Trot, Canter, and Gallop. Some have five. The gallop is the fastest of these.
A walking gait, used for pleasure riding, may be as slow two miles per hour.
The trot consists of two speeds, a jog trot and a working trot. A jog trot is slow, and again a pleasure gait. A working trot is faster and used for pulling carts or other vehicles, or covering distances at a pace the horse can maintain for a long time.
A canter is a smooth, easy-to-ride run, slower than a gallop, faster than a trot, although many horses can execute a very slow canter in a show ring. This is a particularly enjoyable gait for riding.
A gallop is a fast, full-out run, intended to cover distances, but with limits in how long the horse is able to maintain it. This is the gait at which a strong horse can run 15 to 30 miles per hour.
Horses are selectively bred for differing abilities. An American quarterhorse is bred for its agility, common sense while working, and speed - at the quarter mile, as its name implies. These horses are initially bred for ranch work, for working cattle, and for trail work, though they are versatile and often used for other purposes.
These are called stock horses, and others fit that classification: appaloosa, paint, and captured mustangs, for example.
The thoroughbred, the breed seen at races such as the Kentucky Derby, is bred for stamina and speed. Again, they are also useful in other capacities, such as jumping and ranch work. While quarterhorses may reach high speeds and maintain them for a quarter mile, the thoroughbred can maintain high speeds for greater distances.
These horses tend to be leaner, longer, and taller. Thoroughbreds have been used to improve other horse types by breeding them to be taller, leaner, and to have more stamina.
Horses are conditioned for a particular activity by feeding precise nutritional values, exercising to improve quality desired, and training them to cooperate in that activity.
A thoroughbred is fed high-protein grain and grasses, and exercised by running.
A quarterhorse is exercised and fed for agility and short-term speed. He needs to develop more muscle, in the same way a gymnast needs more muscle than a marathon racer.
In professional circles, food is monitored and scientifically engineered to provide maximum value for the specific purpose. A riding horse needs to be fed according to how he is used and how much exercise he receives. In many cases a horse kept for pleasure riding does well on grass hay and frequent, mild exercise. He is not expected to run 30 miles per hour, nor will he.
Conformation is a term that refers to how well a horse is built and how closely it matches the breed standard. This is important when we discuss speed, because a horse with certain types of flawed conformation will not be able to work as hard or run as fast as those without flaws.
A horse with small nostrils will not be able to draw in as much oxygen as one with wide, flaring nostrils. One with a narrow chest (the area of its torso where a saddle girth attaches) will not be able to take as much air into his lungs. A horse with a too-narrow flank will not eat as much energy-supplying hay or grass at a time and won’t have as much stamina.
Leg shape and position are important. Learning about horse conformation is important to a horseman, and will make a huge difference in performance. A horse whose back legs stand under, rather than directly beneath his hips may be very agile as a cow pony, but be unable to run for long distances and may suffer injuries related to the flaw.
Well fed and cared for, a good horse can cover 25 to 30 miles per hour. A great racing horse can run forty-five to fifty miles per hour. It all depends on what breed he is, how he’s fed and exercised, and how well his conformation fits the standards for his breed.