How much does your horse weigh?

What the number means

The heart girth formula turns two tape measurements into a body weight in pounds. Girth squared times length behaves like a volume in cubic inches, and the divisor turns that volume into pounds; it is an empirical constant from the extension sheets, not a physical law. The estimate is good enough to plan feed and a hay order, but it is an estimate; a scale is the only measurement, and your veterinarian should have the real weight for any medication.

Formula and variables

Weight (lb) = heart girth (in) × heart girth (in) × body length (in) ÷ K. The divisor K is 330 for a mature horse (University of Arkansas Extension and Oregon State Extension), 301 for a yearling and 280 for a weanling (Oregon State). In the metric mode your centimeters are converted to inches first, and the pounds are converted back to kilograms, so the answer is the same horse either way. The forage table multiplies the estimated weight by 1, 2 and 2.5 percent, the figures Alabama Extension gives for the minimum, the recommended target and the free-choice intake.

Worked example

Oregon State’s weight calculator works a horse with a heart girth of 70 inches and a body length of 78 inches. 70 × 70 × 78 = 382,200, and divided by 330 that is 1,158 pounds. The sheet prints 1,274 pounds: that is the same product divided by 300 (1,274 pounds), which is the divisor for cattle and sheep on the same sheet, so the example has a slip and the formula in its text, 330, is the one to use. A second horse with a 74-inch girth and a 68-inch body length weighs 1,128 pounds. At a 2 percent forage rate that horse eats 22.6 pounds of dry matter a day, 25.1 pounds of hay as fed.

Common mistakes and limits

First, the tape. Arkansas Extension prefers plastic tapes over cloth, and metal tapes are the least desirable because they can cut the horse. A girth taken at the wrong spot or a body length measured with a slack tape changes the result a lot, since the girth enters squared: a 2-inch error on a 74-inch girth moves a 1,000-pound estimate by about 5 percent. Second, the horse should stand square; Arkansas notes that a horse that will not stand still gives an inaccurate measurement. Third, the formula is not for every horse. Arkansas says it may not be highly accurate for pregnant mares or for a horse with extreme conformational irregularities, and the younger-horse divisors are tied to age groups the sheet does not define in months, so a growing horse close to the boundary is a guess. Fourth, weight is not condition: Alabama Extension scores body condition on the Henneke scale from 1 to 9 by looking at and feeling fat cover, and most horses should be a 5 or a 6.

How the forage numbers work

Alabama Extension says the average horse left to itself eats 2 to 2.5 percent of its body weight in dry matter a day, some more than 3, and that the absolute minimum is 1 percent, usually reserved for horses in heavy work on high-concentrate diets. Its recommended starting point is about 2 percent. For a 1,000-pound horse that is 10, 20 and 25 pounds of dry matter a day, or 300, 600 and 750 pounds in 30 days. Hay is about 90 percent dry matter, so the 2 percent target is 22.2 pounds of hay a day as fed, and 13.3 fifty-pound bales in 30 days. These numbers are for hay or pasture only and assume none is wasted.

How do I estimate my horse's weight without a scale?

Measure the heart girth in inches, run the tape all the way around the horse using the highest part of the withers, and measure the body length in inches from the point of the shoulder straight back along the side to the point of the buttock. Then weight in pounds = girth × girth × length ÷ 330. That is the formula in the University of Arkansas Extension sheet. A horse with a 74-inch girth and a 68-inch body length comes out at 1,128 pounds.

How accurate is the heart girth formula?

The Arkansas sheet calls it more reliable than judging by eye, but says it may not be highly accurate for pregnant mares or horses with extreme conformational irregularities. The measuring matters as much as the formula: the horse should stand squarely, the body length is easy to get wrong, and Arkansas suggests having one person hold the horse and two measure. If you want to follow weight over time, measure at the same time of day, preferably in the morning before feeding. Taking your horse to a scale once, for example at a vet clinic, shows how far off the formula is for that horse.

What divisor do I use for a yearling or a weanling?

The Oregon State Extension weight calculator uses 330 for a mature horse, 301 for a yearling and 280 for a weanling, because younger horses carry less weight for the same measurements. With a 60-inch girth and a 55-inch body length that is 600 pounds with 330, 658 with 301 and 707 with 280.

How much hay should a horse eat in a day?

Alabama Extension gives about 2 percent of body weight per day, in dry matter, as a starting target, with 1 percent as the absolute minimum, which is normally reserved for horses in heavy work on high-grain diets. It adds that horses left to themselves will eat 2 to 2.5 percent, and some more than 3. For a 1,000-pound horse that is 10 pounds at the minimum, 20 at the target and 25 free choice, in dry matter.

Is that pounds of hay or pounds of dry matter?

Dry matter. Alabama Extension puts the dry matter of hay at roughly 90 percent, so the 20 pounds of dry matter for a 1,000-pound horse at 2 percent is 22.2 pounds of hay as fed. The Alabama table counts 12 fifty-pound square bales for 30 days at 2 percent for a 1,000-pound horse, which treats a pound of hay as a pound of dry matter; the calculator shows the as-fed figure, 13.3 bales, to be safe. Waste comes on top: see the hay needed calculator.

What body condition should my horse have?

The weight formula says nothing about fat. Alabama Extension describes the Henneke body condition score as a visual and tactile appraisal of fat from 1 to 9 and says most horses should be a 5 or 6 for optimal health. Other extension services accept a somewhat wider band for some horses, and a pregnant mare or a performance horse can differ, so ask your veterinarian what is right for yours. If the weight and the score together move in the wrong direction, change the feed gradually.

For general information only, not veterinary advice. Ask your veterinarian before changing a horse’s diet, especially a horse that is underweight, overweight, pregnant or ill. Sources: University of Arkansas Division of Agriculture Cooperative Extension, M. Russell, “Estimating a Horse’s Body Weight”; Oregon State University Extension, “Weight Calculator” (sheep and goat, pig, horse and cattle formulas); Alabama Cooperative Extension System, ANR-3153 “Estimating & Supplying Equine Forage Requirements” (C. Heaton, Auburn University; Tables 1 and 2), all read October 28, 2026. The University of Tennessee sheet SP795 could not be opened. Related: hay needed calculator for the winter order, stocking rate calculator for the pasture, pet calorie calculator and fence calculator. How we check our calculators.