Measure the heart girth and the body length (shoulder point to buttock point) in inches, then weight in pounds = girth × girth × length ÷ 330. A horse with a 72 in girth and 66 in length works out to 72 × 72 × 66 ÷ 330 ≈ 1,037 lb, or about 470 kg. Expect it within roughly 3–5% of a scale for adult light breeds.
Most barns have no livestock scale, yet dewormer doses, sedation, feed rations and trailer loading all depend on body weight. This calculator turns two tape measurements into an estimate: heart girth, taken around the barrel behind the elbows, and body length, from the point of the shoulder to the point of the buttock. Enter both in inches or centimetres and it returns the weight in pounds and kilograms, the working, and a daily forage band of 1.5–2.5% of body weight. The 330 divisor was fitted on adult light horses, so foals, miniature horses, heavily pregnant mares and draft breeds can read noticeably off. Measuring the same horse every few weeks with the same tape is a useful way to track gain or loss even where the absolute figure is a little out.
Choose inches for a result in pounds or centimetres for a result in kilograms; both are shown either way.
Run a soft tape around the barrel just behind the elbows and over the withers, and read it as the horse breathes out.
Measure in a straight line from the point of the shoulder to the point of the buttock, with the horse standing square.
The weight, its conversion, the forage range and each step of the sum update as you type.
Result Estimated body weight: 1,037
Weight in pounds: 1,037
Weight in kilograms: 470
Daily forage at 1.5–2.5% of body weight: 16 lb – 26 lb
A typical 15-hand riding horse. The formula puts it just over 1,000 lb, which is the usual weight band for a Quarter Horse of this size.
Result Estimated body weight: 448
Weight in pounds: 989
Weight in kilograms: 448
Daily forage at 1.5–2.5% of body weight: 7 kg – 11 kg
The centimetre readings are turned into inches, run through the same formula, and the 988.6 lb answer is shown as 448 kg.
Result Estimated body weight: 341
Weight in pounds: 341
Weight in kilograms: 155
Daily forage at 1.5–2.5% of body weight: 5 lb – 9 lb
A 50 in girth and 45 in length give about 341 lb, below the range the 330 divisor was fitted on, so the tool flags it.
Weight (lb) = G² × L ÷ 330
GL330The body of a horse is treated roughly as a cylinder: girth squared stands in for cross-section and length for depth, so their product scales with volume. Dividing by 330 calibrates that volume to pounds for mature light horses. Centimetre entries are divided by 2.54 first, and pounds are converted to kilograms by dividing by 2.2046. The forage band multiplies the weight by 1.5% and 2.5%, the usual daily dry-matter intake range for a horse at maintenance.
Studies on adult light horses usually find the girth-and-length formula within about 3–5% of a scale weight, which for a 1,000 lb horse is 30–50 lb either way. It is closer than a commercial weight tape that uses girth alone, because length captures the difference between a short-backed and a long-backed horse of the same girth.
Pass the tape over the withers, down behind the elbows and under the belly, keeping it perpendicular to the ground. Pull it snug against the coat without compressing it, and read the number just after the horse exhales.
Those two bony landmarks are easy to find and do not move with posture, so repeat measurements agree. The 330 divisor was derived with length taken between them; using withers-to-tail or chest-to-tail lengths changes the answer.
It gives a figure, but smaller animals tend to be over-estimated because their bodies are proportionally deeper. Below about 400 lb the tool shows a warning. For minis, a dedicated miniature horse formula or a scale is a better choice.
Horses at maintenance typically eat 1.5–2.5% of their body weight in dry matter per day. For a 1,000 lb horse that is 15–25 lb of hay. Working horses, lactating mares and hard keepers sit at the top of the band; easy keepers at the bottom.
Every two to four weeks is enough to see a trend during a diet or conditioning programme. Use the same tape, the same person and the same time of day, ideally before feeding, so the numbers are comparable.