Horse Weight Calculator — Estimate from Heart Girth & Body Length
Estimate your horse's weight from two simple tape-measure readings. Caslick's formula uses heart girth and body length to give a weight accurate to within 5–10 % of actual — useful for dosing medications and tracking condition.
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Caslick's formula: (Heart Girth² × Body Length) / 330
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Square the heart girth
72² = 5,184 - 2
Multiply by body length
5,184 × 65 = 336,960 - 3
Divide by 330
336,960 ÷ 330 = 1,021Caslick's formula constant for converting the inch-squared × inch product to pounds.
How does this calculator work?
Caslick's formula estimates horse weight as (Heart Girth² × Body Length) / 330, with measurements in inches, giving weight in pounds. Accurate to within 5–10 % for mature horses. Multiply by 0.4536 to convert to kilograms. No scale required — just a soft measuring tape.
Formula
How this is calculated
Caslick's formula (also called the 'string method') is the most widely used field method for estimating horse weight without a livestock scale. Two measurements are taken with a flexible tape: the heart girth — the circumference of the chest just behind the withers and front legs — and the body length — the straight-line distance from the point of the shoulder to the point of the buttock. The formula (HG² × BL) / 330, with measurements in inches, returns weight in pounds.
The method is reasonably accurate for mature horses of typical conformation, with typical errors of 5–10 % against scale weight. It tends to underestimate weight in very heavily muscled breeds (e.g. Quarter Horses in heavy condition) and overestimate in very light breeds or horses in poor condition. For foals and yearlings, separate formulas calibrated for growing horses are more accurate.
Knowing approximate weight is critical for correct drug and supplement dosing, deworming, and feed ration calculation. A weight tape calibrated in pounds is a cheaper alternative to this calculator — both use the same heart girth measurement — but the two-measurement formula is generally more accurate than a single girth measurement alone.
Frequently asked questions
Stand the horse on a level surface with its legs square beneath it. Pass a soft measuring tape around the barrel just behind the elbow and over the withers. Take the measurement after a normal exhale for consistency. Ensure the tape lies flat and snug — too loose or too tight will skew the result.
Body length is measured in a straight line (not over the topline) from the point of the shoulder (the bony protrusion at the front of the scapula) to the point of the buttock (the pin bone / tuber ischii). Have a helper hold the zero end at the shoulder while you pull the tape straight back. The horse must be standing square.
For mature, average-conformation horses the formula is typically within 5–10 % of actual scale weight, which is accurate enough for most practical purposes such as deworming doses and general feed rations. For precise drug dosing (e.g. sedation or anaesthesia), use an actual livestock scale if one is accessible.
TG we-Calculate Editorial Team. (2026). Horse Weight Calculator — Estimate from Heart Girth & Body Length [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/horse-weight-calculator
TG we-Calculate Editorial Team. "Horse Weight Calculator — Estimate from Heart Girth & Body Length." TG we-Calculate. 2026. https://we-calculate.com/calculator/horse-weight-calculator.
TG we-Calculate Editorial Team, "Horse Weight Calculator — Estimate from Heart Girth & Body Length," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/horse-weight-calculator
@misc{wecalculate_horse_weight_calculator, title = {Horse Weight Calculator — Estimate from Heart Girth & Body Length}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/horse-weight-calculator}}, year = {2026}, note = {TG we-Calculate} }
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