How much weight can a horse carry? The 20 percent rule

Where the 20 percent guideline comes from

The rule of thumb is that a horse can carry about 20 percent of its body weight, and and it is repeated widely. Research that has tested it gives a more mixed picture than the rule suggests.

A 2026 survey in the Journal of Equine Veterinary Science of 134 riders in Finland describes 20 percent as the commonly cited maximum. The average rider and horse in that survey came to a ratio of 12.9 percent, and riders considered 12.1 percent suitable. So the typical rider in the survey was well below 20 percent.

Rider plus saddle, not the rider alone

The load is everything the horse carries: the rider, the saddle, the pad, the bridle and anything in saddle bags. In a 2017 Icelandic horse study the ratio was calculated between the rider including the saddle and the horse. Count it that way and the number goes up by the weight of your tack.

To work it out, divide the rider and tack by the horse's weight and multiply by 100. A 1,000-pound horse carries 200 pounds at 20 percent, and 150 pounds at 15 percent. Use a measured weight if you can: in a study of farm managers and veterinarians, visual guesses of horse weight were low 87.5 percent of the time.

What the studies show

In a 2017 study, eight experienced Icelandic school horses were ridden with the ratio rising from 20 to 35 percent. Heart rate, blood lactate, breathing rate and body temperature all went up. The horses worked mainly aerobically until the ratio reached about 22.7 percent, but the individual limit ranged from 17 to 27.5 percent and was linked to back body condition score, not to horse size. Heart rate, breathing and hematocrit were back to resting values within 30 minutes, while lactate and rectal temperature were not. The study used eight horses and one rider, so it shows a pattern, not a safe load for every horse.

A 2025 study of 16 Icelandic tour horses found a relatively low physiological response at 20 to 35 percent, and that a wider chest, an uphill build, a straight back line and a smaller hock circumference were associated with higher carrying capacity. Another 2025 study found that a standard treadmill test did not estimate a horse's weight-carrying capacity, and noted there is no standardized method to estimate it.

A 2020 crossover study of 20 horse and rider pairs added 15 and 25 percent to the regular rider's weight during a dressage test and found no significant short-term changes in stress hormones, heart rate or gait symmetry. The authors warn that the ratios stayed at 15 to 23 percent and the exercise was light, so the result should not be applied to other ratios or harder work.

Fitness, age, back and type matter

The studies above used healthy, adult, fit horses. A horse that is young, old, out of shape, overweight, thin or has a weak back or a lameness is not the same case, and a ratio that is fine for one may be too much for another.

Saddle fit matters as much as the number. An extension article on saddle fit says a poorly fitting saddle can make a horse show displeasure, hurt performance or cause sores, and that bar contact changes once the rider's weight is added. The extension article says a saddle that bridges, meaning it does not touch the back in the middle of the bars, puts excessive pressure on the withers and the loin. A separate study of 128 horses found the saddle slipped consistently to one side in 54 percent of horses with hindlimb lameness, so a saddle that keeps slipping is a reason to call the vet.

Signs a horse is struggling

Researchers measure heart rate, breathing rate, temperature and lactate. At the barn you can watch the plain version: a horse that breathes hard or stays hot for a long time after work, recovers slowly, or is stiff or sore the next day may be finding the load too much. In the 2017 study, heart rate, breathing and hematocrit returned to resting values within 30 minutes of the test, so a horse that is slower than that deserves a closer look.

Look at the back as well. Dry spots on either side of the withers, dry spots with raised skin, rubbing or pressure sores, or displeasure while being ridden can all point to a poor fit. The extension article says soreness in the loin may not be visible and has to be found by feeling the back.

How to decide

Weigh or measure the horse, add the rider and the tack, and work out the ratio. If it is near or above 20 percent, consider a lighter load, easier work or a larger horse. Ask your vet and an experienced saddle fitter, especially for a young, older or unfit horse.

Call your veterinarian if the horse is lame, sore, loses weight, stays hot or breathes hard for a long time after work, or if the saddle keeps slipping to one side.