Weight (lbs) = Heart Girth² × Body Length / 330
The most practical field method uses heart girth (circumference at the withers, behind the elbow) and body length (point of shoulder to point of buttock): Weight (lbs) = Girth² × Length / 330. This formula is accurate to ±5% for adult horses. Weigh tapes calibrated for horses can provide a quick girth-only estimate but are less accurate. Average weights: pony 400-600 lbs, Quarter Horse 1000-1200, Thoroughbred 900-1100, Draft Horse 1500-2200. Accurate weight is essential for: drug dosing (especially dewormers — underdosing promotes resistance), feed calculation, and monitoring health. Weigh monthly; sudden weight changes may indicate illness.