Horse Weight from Girth Calculator
You can estimate an adult horse's body weight with a soft tape and the formula taught by university equine extension programs: weight in pounds equals heart girth squared times body length, divided by 330, with both measurements in inches. Heart girth is the circumference just behind the front legs and withers, and body length runs from the point of the shoulder to the point of the buttock. Because the constant differs for ponies and young horses, the divisor is editable (use 330 for mature horses). The result is a practical estimate for feeding and dosing, generally within about 10 percent of a livestock scale.
330 for mature horses; ponies and foals use other values.
Horse weight formula
Weight (lb) = (heart girth ^ 2 * body length) / divisor
Weight (kg) = weight (lb) / 2.2046226
Heart girth and body length are both in inches. The divisor of 330 applies to mature horses. The kilogram figure is a straight unit conversion of the pound estimate.
Measuring context
- Use a flexible tape and measure on level ground with the horse standing square.
- Take heart girth at the end of a normal exhale for a consistent reading.
- Body length is point of shoulder to point of buttock, not nose to tail.
- The estimate suits adult horses; growing horses and ponies need different constants.
- For precise medication dosing a calibrated livestock scale is preferred.
Horse weight: frequently asked questions
How do you estimate a horse's weight from a tape measure?
The standard adult-horse formula used by university extension programs is weight in pounds equals heart girth squared, times body length, divided by 330, with both measurements in inches. Heart girth is the circumference just behind the front legs and withers; body length runs from the point of the shoulder to the point of the buttock.
Where exactly do I measure heart girth and body length?
Heart girth is measured as the full circumference of the chest just behind the elbows and the withers, with the tape snug at the end of a normal breath. Body length is the straight-line distance from the point of the shoulder to the point of the buttock (the rear of the pelvis).
Is the divisor always 330?
For mature horses the divisor 330 is the widely published value. Ponies and growing young horses use different constants, so this calculator keeps the divisor editable. Use 330 for adult horses unless your extension source specifies otherwise for your animal's type.
How accurate is the girth-and-length method?
It is a good practical estimate, typically within roughly 10 percent of a livestock scale for a normally conditioned adult horse. It is more accurate than a weight tape alone because it includes body length. A calibrated scale remains the gold standard for precise dosing.
Why does estimating horse weight matter?
Body weight drives correct deworming and medication doses, feed rations, and monitoring of condition over time. Many products are dosed per pound or kilogram, so an accurate weight estimate helps avoid under- or over-dosing.
Official sources
- University of Minnesota Extension: Horse care and nutrition.
- Michigan State University Extension: Horses.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.