Horse Weight Estimate Calculator
When no livestock scale is available, an adult horse's weight can be estimated from two tape measurements: the heart girth around the barrel just behind the front legs, and the body length from the point of shoulder to the point of buttock. This calculator applies the standard heart-girth equation. Measure in inches; the result is in pounds, with a kilogram conversion shown. The divisor is user-editable so you can switch between the adult-horse, yearling and pony constants.
Heart-girth formula
Weight (lb) = (girth^2 * length) / divisor
Weight (kg) = weight (lb) * 0.45359237
Girth and length are in inches. The divisor is 330 for adult horses, about 301 for yearlings and about 299 for ponies; enter the value that matches your animal.
Worked example
A horse with a 75 inch girth and 65 inch length, adult divisor 330: weight = (75 * 75 * 65) / 330 = 365,625 / 330 = 1,107.95 lb. In kilograms: 1,107.95 * 0.45359237 = 502.56 kg.
Horse weight: frequently asked questions
How do you estimate a horse's weight without a scale?
A widely used method measures the heart girth (around the barrel just behind the front legs) and the body length (point of shoulder to point of buttock), both in inches. The estimate in pounds is (girth squared times length) divided by 330 for an adult horse. This is an estimate, not a substitute for a livestock scale.
Where does the divisor 330 come from?
330 is the constant in the heart-girth equation for adult horses published by agricultural extension services. The constant differs for ponies (around 299) and yearlings (around 301), so it is left as a user-editable input here. Measurements are in inches and the result is in pounds.
How accurate is the heart-girth estimate?
Tape and girth-length estimates are generally within roughly 10 percent of true weight for typical adult horses of normal body condition. Accuracy falls for very fat, very thin, pregnant or unusually shaped animals. For dosing or sale, confirm with a calibrated scale where possible.
Official sources
- U.S. Department of Agriculture: National Agricultural Library (livestock and equine reference).
- The pound-to-kilogram factor 0.45359237 is the exact international avoirdupois pound definition (NIST).
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.