How this calculator works
Mature livestock at maintenance eat a predictable share of their body weight in forage every day — about 2–2.5% for horses and beef cattle, closer to 3% for goats, and more across the board in hard cold. This tool multiplies that daily need across every animal group you add, then across your no-pasture days, to get a base tonnage before any losses are counted.
That base number is almost never what you should actually buy. Two losses get added on top: storage loss, which runs about 5% for hay kept inside a barn but can climb toward 30% for hay left outside on bare ground uncovered, and feeding waste, which depends entirely on how the hay is offered. Square bales fed on the ground lose about 13% to trampling and soiling versus roughly 3% in a basket feeder or 5% in a hay rack; round bales set out with no feeder at all can lose more than half their weight before an animal eats any of it, against roughly a fifth with a feeder. Those two losses compound — multiplied together, not just added — which is exactly why homemade back-of-envelope estimates run short partway through winter.
Bale counts round up, because you can't buy two-thirds of a bale — and because hay bought in June, right after cutting, is reliably cheaper than hay bought in January, when supply is whatever's left in someone's barn. If you mix species or add grain to any group, the calculator adjusts each group's daily need separately before combining them, so a mixed horse-and-goat herd gets the right total rather than an average. Compare quotes in the hay price converter, check the order in the hay storage calculator, or test bale formats in the round-vs-square comparison. Entering a bale price unlocks average per-head costs and loss-dollar figures; adding an actual feeder quote also calculates payback when the plan has positive whole-bale savings. Entering hay already on hand subtracts whole bales from the rounded gross requirement and shows the net bales and cost still to buy. The optional Check my season fields turn entered mid-season stock into an observed disappearance rate, a projected run-out date, and a whole-bale reorder quantity. The storage-upgrade scenario uses entered assumptions for seasonal savings and simple payback; supplier lead time adds an order-by date. The result breaks mixed-herd base need out by group without rounding groups separately. Its A/B scenario comparison is ephemeral, holding two snapshots only in page memory until reload or close.
Method and waste figures follow published university extension guidance (University of Maryland Extension; Penn State Extension; N.C. Cooperative Extension; University of Minnesota). Barn-space volume uses Missouri Extension's 250 ft³/ton square and 310 ft³/ton round planning rates, with Extension Horses independently supporting about 250 ft³/ton for baled hay. Actual needs vary with bale density, dimensions, and stacking; ventilation, access aisles, equipment turning space, wall clearance, and local fire-code space are not included. Estimates only — adjust for body condition, hay quality, and your vet's advice.
Frequently asked questions
How much hay does a horse need per day?
A mature horse at maintenance eats about 2–2.5% of its body weight in hay per day — roughly 20–25 lb for a 1,000 lb horse. Cold weather can push intake toward 3%.
How many bales of hay do I need for winter?
With the page defaults — one 1,000 lb horse, 120 cold-weather days, 50 lb small squares, inside storage, and ground feeding — the result is 72 bales. Selecting a basket feeder lowers it to 65.
How much hay is wasted when feeding on the ground?
Extension studies measured about 13% waste for square bales fed on the ground versus 3–5% in a rack or basket feeder, and up to 57% for round bales fed without a feeder.
Plan the rest of the barn
BaleMath is free to use. Numbers are planning estimates, not veterinary or nutritional advice.