How this calculator works
Choose a hay allocation from an existing ration, or estimate the hay dry-matter allocation as a percentage of body weight. Enter only the hay portion, not total diet intake. Choose allocations appropriate to each group’s class and stage. The calculator neither selects an allocation nor checks nutritional adequacy. There is no automatic grain subtraction or cold-weather multiplier.
Dry matter is the part of hay remaining after water is excluded. Use a forage analysis where available, identify whether the dry-matter value is measured or estimated, and weigh several representative bales. The allocation is multiplied by animal count and days. Dividing that seasonal dry matter by the entered hay dry-matter fraction gives the consumed hay equivalent.
Feeding loss is a share of hay offered; storage loss is a share of incoming hay. To work backwards to a purchase, divide the consumed equivalent by the fraction retained after feeding, then by the fraction retained after storage. Enter losses for your feeding arrangement, hay lot and storage period. A percentage from a different animal species, feeder design or storage duration is not automatically applicable.
Combine all groups before rounding up to whole bales. Purchase weight, price and space use that whole-bale count. The ledger reconciles consumed hay, feeding loss, storage loss and rounding surplus at the same entered dry matter. It does not predict moisture changes, selective nutrient loss or whether weathered hay remains suitable. Assess existing or mixed lots separately.
The example above combines 10 kg/day of horse hay dry matter and 9 kg/day for goats: 2,280 kg over 120 days. With its shared hay lot, losses and 25 kg bales, rounding once gives 119 bales; separate group rounding gives 120. This is inventory arithmetic, not a feeding recommendation.
Body-weight percentages depend on animal class and diet: Extension Horses distinguishes forage from the total ration; Nebraska Extension describes goat intake on a dry-matter basis. Mississippi State Extension explains the dependence of storage losses on conditions and duration. See About & sources for the source record; citations are not endorsements.
On-hand hay reduces the whole-bale purchase. Dated season stock estimates observed disappearance, run-out and reorder quantity. The storage-upgrade scenario uses entered targets for seasonal savings and simple payback; supplier lead time adds an order-by date. Use the price converter, water planner and manure planner. The round-vs-square calculator compares explicit hay-DM purchases.
Barn-space volume uses Missouri Extension planning rates of 250 ft³/ton square and 310 ft³/ton round (US short tons); Extension Horses corroborates the square-hay rate. 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.
The breakdown shows each group’s contribution without rounding groups separately. A/B comparisons keep two snapshots in page memory until reload or close.
Frequently asked questions
How much hay does a mixed herd need per day?
Example: one horse allocated 10 kg hay dry matter/day plus five goats allocated 1.8 kg each totals 19 kg/day: 21.11 kg consumed hay at 90% dry matter, before losses. Not a feeding recommendation.
How many bales of hay do I need for winter?
Example: 19 kg hay dry matter/day for 120 days, 90% hay dry matter, 10% feeding loss, 5% storage loss and 25 kg bales gives 119 bales, rounded once across groups. Not a feeding recommendation.
Does grain automatically reduce the hay allocation?
BaleMath does not automatically subtract grain or calculate a substitution ratio. Use the hay portion of an appropriate existing ration, and seek qualified advice when changing the diet.
Plan the rest of the barn
BaleMath is free to use. Numbers are planning estimates, not veterinary or nutritional advice.