Horse Weight Calculator (heart girth & body length tape method)

Understanding the horse weight calculator — concept and principle

This calculator estimates an adult horse's body weight from two tape measurements, heart girth and body length, using the extension service formula. Owners use it to dose wormers and medicines, plan feed rations and track weight changes when no scale is available.

Girth² × length: with the default inputs the result is ≈ 500 kg (= 1,101 lb).

How it is calculated

Weight (lb) = heart girth × heart girth × body length ÷ 330

Both measurements in inches; centimetres are converted with 1 in = 2.54 cm.
Weight in kg = lb × 0.45359237.
Heart girth: around the barrel just behind the elbows and over the withers. Body length: from the point of the shoulder to the point of the buttock.

The principle

A horse's body is roughly a cylinder. Its volume, and so its weight, grows with the square of the girth (which sets the cross-section) times the length. The divisor 330 was fitted to match measured weights of typical adult horses, so it combines the shape factor and the average density of the body. Because girth is squared, a small error in the girth measurement has a bigger effect than the same error in length.

Worked example

Default inputs: centimetres, heart girth 190 cm, body length 165 cm.

Girth = 190 ÷ 2.54 = 74.8 in; length = 165 ÷ 2.54 = 65 in.
Weight = 74.8 × 74.8 × 64.96 ÷ 330 = 1,101 lb.
In kilograms = 1,101.5 × 0.4536 = 500 kg.

Each point is the calculator re-run with only “Heart girth” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Heart girth	Estimated weight (kg)
47.5	31
95	125
142	281
190	500
238	781
285	1,124
380	1,998

How to read the result

Use the same method, the same tape and the same time of day each time, ideally in the morning before feeding, so changes over weeks are meaningful. The formula is less reliable for foals, pregnant mares, very muscular breeds and horses with unusual build. A weighbridge or clinic scale is best when an exact weight matters, such as for some medications.

Common mistakes

Measuring the girth too far back or with the horse not standing square.
Pulling the tape too tight or leaving it slack.
Measuring length to the tail instead of the point of the buttock.
Using the formula for foals.

Keep in mind: This is an estimate, not a veterinary measurement. Ask your vet for exact dosing of medicines.

Frequently asked questions

How do I estimate my horse's weight without a scale?

Multiply heart girth by itself and by body length in inches, then divide by 330 to get pounds.

Where do I measure heart girth?

Around the barrel just behind the front legs and over the withers.

How accurate is a weight tape?

It is better than guessing by eye, but less accurate than a scale, especially for unusual builds.

Sources: University of Arkansas Cooperative Extension Service (M. Russell), "Estimating a Horse's Body Weight"

Checked 9 Nov 2026. University of Arkansas Cooperative Extension Service (M. Russell), “Estimating a Horse’s Body Weight”: (heart girth × heart girth × body length) ÷ 330 = weight in pounds; measuring instructions and accuracy notes.

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