Estimate body weight without a scale from heart girth and body length — for cattle, horses, and pigs — with the classic tape formulas.
Use this when you need a working weight for dosing, feed budgets, or trailer loading and there is no scale on the place. A tape estimate is far better than an eyeball guess, but a scale is better still.
Measure heart girth around the barrel just behind the front legs, snug but not tight. Body length runs from the point of the shoulder to the point of the buttock (pin bone) on cattle and horses, and from between the ears to the base of the tail on pigs.
Weight tracks body volume, which scales with girth squared times length. A species divisor turns cubic inches into pounds. The common field divisors are 300 for cattle, 330 for horses, and 400 for pigs.
weight_lb = heart_girth_in² × body_length_in ÷ divisor
weight_kg = weight_lb ÷ 2.2046
Steer: heart girth 72 in, body length 66 in → 72² × 66 ÷ 300 = 5,184 × 66 ÷ 300 = 1,140.5 lb (517 kg).
Horse: 75 in girth, 66 in length → 5,625 × 66 ÷ 330 = 1,125 lb.
Pig: 45 in girth, 45 in length → 2,025 × 45 ÷ 400 = 227.8 lb.
Assumptions: average body shape and condition for the species; tape pulled snug at the right landmarks.
Limits: very fat, thin, pregnant, young, or unusually shaped animals can be off by 10% or more. Gut fill changes girth through the day.
Responsibility: use a scale for sale weights and for drugs with narrow dosing ranges; follow your veterinarian's dosing instructions.
For average animals a careful tape estimate is often within about 10% of scale weight. Measure the same way each time to track change over time.
The divisors here are for inches and pounds. Convert cm to inches (÷ 2.54) first, then read kg from the result.
Each divisor is fitted to a group of animals. If a scale check on your stock shows a steady bias, edit the divisor to match.