# Horse weight calculator

> Estimate a horse’s weight from heart girth and body length with the formulas in the Merck Veterinary Manual, for adults, yearlings and weanlings.

Canonical: https://lucernel.com/tools/horse-weight-calculator
Last updated: 2026-09-26

Measure the heart girth and the body length with a soft tape. You get the estimated weight in pounds and kilograms, using the formulas in the Merck Veterinary Manual.

Free, no account. Everything runs in your browser. Nothing you type is sent or stored. Interactive version: https://lucernel.com/tools/horse-weight-calculator

## How it works

Heart girth is measured around the body just behind the shoulder, at the base of the withers. Body length is measured from the point of the shoulder to the point of the rump, with the horse standing square.

For an adult horse (over 2 years), weight in pounds = heart girth × heart girth × body length ÷ 330, in inches. For a yearling the divisor is 301 and for a weanling 280. In centimetres, the adult formula is girth² × length ÷ 11,880 for kilograms.

The Merck Veterinary Manual notes that the formula is closer to real weight than a weight tape but tends to slightly underestimate. Measure the same way each time and the trend is reliable even when the number is a little off.

Formula: Adult: lb = girth² × length ÷ 330 (inches). Yearling: ÷ 301. Weanling: ÷ 280.


## Good to know

- A scale is the only exact method. Use the estimate to follow changes and as a starting point.
- Weight tapes do not suit miniature horses, donkeys or draft horses; treat any girth-based estimate for them with caution.
- Ask your veterinarian before dosing a medicine from an estimated weight.

## Frequently asked questions

### How accurate is a horse weight tape?

Tapes are the least accurate tool and tend to underestimate. The girth-and-length formula is closer, but still slightly low; a scale is the only exact method.

### Where do I measure heart girth?

All the way around the body just behind the shoulder, over the base of the withers, with the tape snug and level.

### How much does a horse eat per day?

The Merck Veterinary Manual puts the maximum daily intake at about 2.5 to 3% of body weight in dry matter. Your veterinarian or nutritionist sets the actual ration.

## Trotley keeps every horse’s record.

Track weight next to vaccination, dental, farrier and feed records for each horse, with reminders and reports for your vet.

- Weight history charts per horse
- Vaccination, dental, farrier and medication records
- PDF reports for the vet or a new owner

[Trotley](https://lucernel.com/apps/trotley)

## Sources (checked 2026-09-26)

- [Merck Veterinary Manual: Nutritional requirements of horses](https://www.merckvetmanual.com/management-and-nutrition/nutrition-horses/nutritional-requirements-of-horses-and-other-equids)