Two tape measurements in — his heart girth and his body length — and his weight out, by the formula a 1988 study fitted to 281 weighed horses, the one the university extension services print. Then what the number is for.
His weight
About 1,125 lb
What the number is for
An estimate from a tape, not a scale. The University of Arkansas’ extension calls the formula more reliable than guessing by eye, and warns it may not be highly accurate for pregnant mares or horses with extreme conformation. If a number matters, such as a medicine dose, weigh him on a scale; most vets have one.
Formula and sources checked 2026-09-25.
Quick answer: with no scale, estimate a horse’s weight from two tape measurements. Multiply the heart girth by itself, then by the body length (point of the shoulder to point of the buttock), then divide by 330. That gives pounds when the tape is in inches. A horse with a 75-inch girth and a 66-inch body length weighs about 1,125 lb. It is the formula Carroll and Huntington fitted in 1988 to 281 horses they measured and weighed, and the one the University of Arkansas’ extension prints.
How to use it
Take the two measurements with a soft or plastic tape, with the horse standing square. The heart girth goes all the way round him, over the highest part of the withers. The body length runs from the point of the shoulder, straight back along his side, round the corner of the hip to the point of the buttock. Put both in, in inches or centimetres, and his weight comes out in pounds and kilograms. The page then turns it into the numbers people usually want it for: hay per day, and the share of his weight a rider and saddle make.
Where the formula comes from
In 1988, C. L. Carroll and P. J. Huntington of Victoria’s Department of Agriculture and Rural Affairs weighed 372 horses of different breeds, heights and body conditions. They measured the girth and length of 281 of them and found weight closely followed girth squared times length: the fit was r² = 0.90. In centimetres and kilograms, the divisor averaged 11,900. In inches and pounds it becomes the 330 the extension sheets print, and the two land within 0.2% of each other.
An r² of 0.90 is a close fit for a tape measure, but it is not a scale. The University of Arkansas’ extension notes the formula may not be highly accurate for pregnant mares or for horses with extreme conformation. It suggests checking it against a scale while you learn; most vets have one.
Measure the same way every time
The formula is also a way to track change over time. For that, Arkansas’ advice is to measure at the same time of day, ideally in the morning before feeding. Keep the tape in the same places and stand him square. A helper on the other side makes the girth easier, and a second pair of hands makes the length easier.
What his weight is for
Most feeding and riding numbers start from it. The University of Maryland’s extension puts hay at 2% of body weight a day, and the feed and hay calculator takes it from there. The most quoted rider guide, Powell’s 20%, is a share of it too, and the rider weight calculator shows what the other studies found. Wormers and medicines are also dosed by weight. That dose is the label’s and your vet’s to give, never a calculator’s, and if the dose matters, weigh him on a scale.