Horse Weight Calculator – How Much Does My Horse Weigh?
Two tape measurements give a good working weight for feeding, worming and medicine doses.
Where to measure
Estimated weight
409 kg
902 lb
Imperial formula check (adult light horse): 899 lb
A weighbridge is the most accurate option – use this as a good working figure.
Usually within about 10%. Less reliable for very fat, pregnant or unusually built horses.
Why knowing the weight matters
Almost everything you give a horse is dosed by weight: forage, hard feed, wormers, bute, sedatives and antibiotics. Owners routinely underestimate a horse's weight by fifty kilograms or more, which means wormers get under-dosed – a genuine driver of resistance – and diets get planned around a number that does not exist. Ten minutes with a soft tape measure fixes that.
How to measure
- Stand your horse square on level ground, ideally before their morning feed.
- Heart girth: pass the tape around the barrel, just behind the withers and behind the elbows. Snug, not tight, at the end of a breath out.
- Body length: measure in a straight line from the point of the shoulder to the point of the buttock.
- Take each measurement twice and use the average.
The formula
Weight in kilograms equals heart girth in centimetres squared, multiplied by body length in centimetres, divided by a constant that reflects the horse's build. Adult light horses use 11,880; ponies 10,764; heavy or draught horses 8,676; yearlings 10,836 and weanlings 10,080. In imperial, girth in inches squared multiplied by length in inches, divided by 330, gives pounds for an adult light horse.
Worked example
A riding horse with a 180 cm heart girth and a 150 cm body length: 180 × 180 = 32,400; multiply by 150 to get 4,860,000; divide by 11,880 and you get about 409 kg. If that same horse were a stocky cob, the pony constant would give a noticeably higher figure – which is why choosing the right type matters.
The limits of the formula
These equations were developed on horses of fairly normal build, so they lose accuracy at the extremes: very obese horses, heavily pregnant mares, very fine thoroughbreds and rapidly growing youngstock. Treat the answer as a good working figure, not gospel. A public weighbridge, or the one at many veterinary practices and feed merchants, is always the most accurate option and is well worth using once to check how close your tape measurements land.
Tracking change
Measure monthly, on the same day of the month, and write it down alongside a fat score. The trend matters more than any single reading: a steady climb through spring is the signal to reduce grazing or increase work, long before laminitis becomes a risk.
Frequently asked questions
How do you work out a horse's weight without a weighbridge?
Measure the heart girth and body length, then use weight in kg = girth in cm squared × length in cm ÷ a constant. The constant depends on the type of horse – 11,880 for an adult light horse.
Where exactly do I measure the heart girth?
All the way around the barrel, just behind the withers and behind the elbows, with the tape snug but not tight. Take the measurement at the end of a normal breath out.
Where do I measure body length?
From the point of the shoulder to the point of the buttock, in a straight line, with your horse standing square on level ground.
How accurate is the formula?
Usually within about ten per cent for a typical adult horse of normal build. It is less accurate for very fat, very pregnant, very young or unusually shaped horses. A weighbridge is always the most accurate option.
Are weight tapes any good?
They are handy for tracking change over time but tend to be less accurate than the formula, especially for ponies and cobs. Use the same method each time so the trend is meaningful.
Why do I need my horse's weight?
Feed, forage, wormers and most medicines are dosed by body weight. Underestimating weight is one of the most common causes of under-dosing wormers.
How often should I weigh?
Monthly is ideal, and fortnightly during a weight-loss programme or in spring when the grass comes through.
Estimates only – not a substitute for advice from your vet.
Last reviewed: 22 September 2026