Horse Weight Calculator

What this calculator actually does

It applies published tape-measure equations to the numbers you enter. It does not weigh your horse. Every result on this page is an estimate produced from two or four body measurements.

The two-measurement option uses the long-established girth and length equation: heart girth in inches, squared, multiplied by body length in inches, divided by a constant. That constant is 330 for adult light riding horses.

The four-measurement option uses the breed-type equations published by University of Minnesota Extension. Those add height at the withers and neck circumference, because a draft horse and an Arabian with the same girth do not weigh the same.

If you enter centimeters, the tool converts to inches first by dividing by 2.54, because both equation families are published in inches and pounds. Kilograms come from pounds multiplied by 0.45359237. The result panel shows every step with your numbers in it.

How to take the measurements

Stand the horse square on level ground. Use a soft dressmaker's tape, not a stiff builder's tape. Take each measurement twice and use the average if the two readings differ.

• Heart girth. Pass the tape around the barrel, over the highest point of the withers, and bring it as close behind the elbows as it will sit. Snug, not tight. Read it as the horse breathes out.
• Body length. From the point of the shoulder straight back to the point of the buttock. This usually needs two people. The tape does not have to be parallel to the ground.
• Height at withers. Ground to the top of the withers. If the horse is shod, subtract the shoe height, as the Minnesota researchers did.
• Neck circumference. Around the neck at the halfway point between the poll and the withers.

Small differences in where you place the tape move the answer. Girth is squared in the two-measurement equation, so a one inch error in girth shifts the result far more than a one inch error in length.

Which horses each equation was built for

The girth and length equation was developed and tested mainly on adult light riding horses. Outside that population it drifts, and it drifts in ways nobody has published a correction for.

• Ponies, drafts, warmbloods, Thoroughbreds and Miniatures. Use the four-measurement option. Minnesota published a separate equation for each of these, fitted to horses that were actually weighed on a livestock scale.
• Yearlings and weanlings. The 301 and 280 divisors are published by university extension for growing horses, but no validation study or published error figure sits behind them. Treat those numbers as rough, and watch the trend over weeks rather than the single figure.
• Suckling foals. Not covered here. Ask your vet or use a scale.
• Pregnant mares. Not covered. Every one of these equations was built on non-pregnant horses. In late gestation the girth includes the foal and its fluid, so the estimate reflects a pregnancy, not body condition.
• Saddle-type and gaited horses. Minnesota publishes an equation for this group. It is not included here, so use their page directly.

You will see divisors like 299 for ponies quoted around the internet. There is no accessible study behind that number, so this page does not use it.

How far off can it be?

The honest answer is further than most people expect. In a study of 600 horses of different ages, heights and breeds, the girth and length formula averaged 98.6 percent of true scale weight, with a standard deviation of 10.6 percentage points.

An average that good with a spread that wide means the same thing as this: across a whole yard the formula is close, but your individual horse can sit ten percent or more either side of the figure on this screen. On a 500 kg horse that is 50 kg.

Weight tapes, which use girth alone, tend to be less accurate again and generally read low, more so on heavier horses. Eyeballing a horse is the least accurate method of all. Owners of drafts and warmbloods were out by roughly 52 kg on average when asked to guess.

When an estimate is not good enough

Some decisions need a calibrated livestock scale rather than a tape.

• Medication dosing. Dose by an accurate bodyweight. Underdosing wormers drives anthelmintic resistance, and for other drugs the consequences depend entirely on the medicine. Confirm the dosing weight with your vet.
• Weight loss or gain you cannot explain. A horse dropping condition without a diet change needs a veterinary exam, not a tape measure. Bring your dated measurements with you.
• Growing horses on a monitored growth curve. Growth rate matters more than any single figure, and the growing-horse divisors are the weakest part of this tool.
• Any pregnant mare, or any horse being managed for laminitis, EMS or PPID. Those decisions belong with your vet.

Many equine clinics, larger feed stores and some haulage yards have a scale you can book. It is worth doing once, so you learn how far your tape estimate sits from reality for your horse.

Getting numbers you can compare

Consistency beats accuracy for day-to-day management. If you always measure the same way, the change between measurements is meaningful even when the absolute figure is not.

• Measure at the same time of day, ideally in the morning before feeding. Gut fill moves girth.
• Use the same tape and the same person each time.
• Record the date and both raw measurements, not just the calculated weight.
• Monthly is enough for a settled horse. Weekly if you are actively changing the diet.

Pair the number with a body condition score. Weight tells you how much horse there is; condition scoring tells you how much of it is fat. A fit 500 kg horse and a fat 500 kg horse need very different feeding.

Once you have a working figure, our horse feed calculator turns it into a forage estimate, and our horse deworming calculator covers the fecal egg count approach your vet will want to see.

Sources

• University of Minnesota Extension, Estimating actual and ideal bodyweight of adult horses — the breed-type equations, coefficients and measurement points used in the four-measurement option. Reviewed 2024.
• University of Minnesota Extension, Feeding the weanling and yearling horse — the 280 and 301 divisors.
• University of Tennessee Extension SP795, Evaluating Your Horse's Body Weight and Condition — the 330 divisor, measurement method and a worked example.
• Ellis and Hollands, Accuracy of different methods of estimating the weight of horses, Veterinary Record 1998 — the 98.6 percent mean and 10.6 point standard deviation across 600 horses.
• Wagner and Tyler, A Comparison of Weight Estimation Methods in Adult Horses, JEVS 2011 — states the established formula and shows formula and tape estimates differ significantly from scale weight.
• Milner and Hewitt, Weight of horses: improved estimates based on girth and length, Canadian Veterinary Journal 1969 — early derivation of the girth and length approach.
• Martinson et al., Estimation of body weight and development of a body weight score for adult equids, Journal of Animal Science 2014 — Arabian, pony and stock equations.
• Catalano et al., draft and warmblood bodyweight equations, JEVS 2016 — draft and warmblood equations and the 28 kg root mean square error.
• Catalano et al., Miniature, saddle-type and Thoroughbred bodyweight equations, JEVS 2019 — Miniature and Thoroughbred equations.
• Grimwood et al., Factors Affecting Weigh Tape Reading in the Measurement of Equine Body Weight, Animals 2023 — weight tapes generally underestimate, more so on heavier horses.
• AAEP Internal Parasite Control Guidelines — incorrect dose from inaccurate bodyweight estimates as a cause of reduced anthelmintic efficacy.
• UF/IFAS Extension VM251 — use an accurate bodyweight when administering anthelmintics.

Educational estimate only. This calculator does not weigh your horse and is not veterinary advice. A calibrated livestock scale is the most accurate method available. Confirm dosing weights with your veterinarian, and contact them about any weight change you cannot explain.