Hay Calculator

How hay math works

Hay planning starts from body weight: university extension programs put the forage baseline at roughly 1.5 to 2 percent of body weight per day. For a 1,000-pound horse that is 15 to 20 pounds of hay daily — about a third of a typical 50-pound square bale. The calculator defaults to 2 percent, the more common planning figure for horses on hay alone, and lets you adjust within the published range.

Cold changes the math. Fermenting forage in the hindgut produces heat, so hay — not grain — is how a horse warms itself. The standard rule of thumb adds about 2 pounds of hay per day for every 10 degrees Fahrenheit below freezing. Turn on the cold-weather setting and enter the overnight low you are planning around, and the calculator builds the winter bump into every total.

What you buy has to exceed what gets eaten. Between feeding waste (hay pulled out of feeders and trampled) and storage losses (moisture, mold, the bottom layer on bare ground), a margin of 10 to 15 percent is a common planning figure — and outdoor storage can push losses toward 40 percent. The waste setting adds your margin to the purchase total, then the calculator converts everything into bales using your real bale weight.

Baseline, cold-weather rule, and waste figures per: Univ. of Minnesota Extension — Ten ways to stretch your horse's hay supply · Univ. of Maryland Extension — Calculating Your Horse's Winter Hay Needs · NDSU Extension — Feed Horses Properly in Winter (≈2 lbs per 10°F below 32°F)

Hay questions, answered

Why is hay calculated as a percentage of body weight?

Forage is the foundation of a horse's diet, and university extension guidance puts the baseline at roughly 1.5 to 2 percent of body weight in forage per day — 15 to 20 pounds of hay for a 1,000-pound horse. The percentage scales naturally from ponies to drafts, which is why hay math starts from body weight rather than a flat number per horse.

Why do horses need more hay in winter?

Digesting forage produces heat, so hay is how a horse keeps itself warm. The common rule of thumb from extension programs is roughly 2 extra pounds of hay per day for every 10 degrees Fahrenheit below freezing, more if the horse is wet or has no shelter. That is why winter hay planning at the same herd size needs meaningfully more hay than summer.

How much does a bale of hay weigh?

It varies more than people expect: small square bales commonly run anywhere from about 40 to 120 pounds depending on the hay type, baler settings, and how tightly they are packed. The calculator defaults to 50 pounds, but the most reliable move is to weigh a few of your own bales on a bathroom scale and use that number — bale-count math is only as good as the bale weight.

How much extra hay should I buy beyond the calculation?

Plan a margin on top of what gets eaten. Feeding waste alone commonly runs around 10 to 15 percent, and storage losses for hay stored outside or on bare ground can climb toward 40 percent. The calculator's waste setting adds that margin to the purchase total — raise it if your hay lives outdoors under a tarp, and remember that running out mid-winter is the expensive outcome.

What if I don't know my horse's weight?

Estimate it first — the math here starts from body weight. If you don't have access to a livestock scale, the girth-and-length method gets you a usable planning number from two tape measurements; our horse weight calculator walks through it. A typical light riding horse lands around 900 to 1,200 pounds, but measuring beats guessing.