Horse Weight Calculator
A horse’s body weight from a tape around the heart girth and its body length — for feed rations and dosing when there is no scale.
Measure the heart girth just behind the elbows, over the withers, and the body length from the point of the shoulder to the point of the buttock.
How the horse weight calculator works
Measure the heart girth just behind the elbows, over the withers, and the body length from the point of the shoulder to the point of the buttock. Weight in kilograms ≈ girth² × length ÷ 11,880 with centimetres (girth² × length ÷ 330 gives pounds with inches). It is usually within 5–10% for an adult horse in average condition; ponies and heavy breeds differ a little.
Formula: kg = girth (cm)² × length (cm) ÷ 11,880; lb = girth (in)² × length (in) ÷ 330
Worked examples
| Inputs | Estimated weight | Note |
|---|---|---|
| 190 cm girth, 170 cm long | 517 | 517 kg |
| 75 in girth, 67 in long | 1,146 | 1,142 lb |
| A pony: 140 cm girth, 120 cm long | 198 | 198 kg |
FAQFrequently asked questions
Why not just use a weight tape?
A weight tape reads girth only and assumes an average body length; adding the actual length improves the estimate, especially for horses unusually long or short in the body.
How much hay should a horse eat?
About 1.5–2.5% of body weight in forage a day — 8–12 kg of hay for a 500 kg horse — with hard feed only as work or condition requires.
Why do I need the weight for worming?
Wormers and most medicines are dosed per kilogram. Guessing a horse’s weight by eye is typically 10–20% out — enough to under-dose and encourage resistance.
How accurate is it?
Usually within 5–10% for adult horses in average condition. Foals, very fat or very lean horses and heavy draught breeds are less well described by a single formula.
Where these figures come from
- NCBI Bookshelf — Molecular Biology of the Cell — growth kinetics and molecular conventions
- Wellcome Sanger Institute — a leading UK genomics institute
Last checked: September 2026. Formulas are the standard textbook forms; assumptions are stated on each page because they are where these models break.