Horse Hay Feed Requirement Calculator

Introduction: what a winter of hay actually costs

Feeding a horse looks straightforward from the outside: put hay in front of it and let it graze. Getting the quantity right is a balancing act between digestive health, body condition, storage space and money. Too little forage risks gastric ulcers, colic and stereotypies; too much drives obesity, insulin dysregulation and a hay bill that quietly doubles. This calculator turns the standard equine intake guideline into three numbers you can act on: the dry matter your horse needs each day, the as-fed weight of hay that corresponds to, and the number of bales to buy for whatever period you are planning.

Horses evolved as trickle feeders, taking small amounts of fibrous forage across most of the day. Domesticated horses usually rely on conserved hay for part or all of that intake, especially through winter or when pasture is short. The National Research Council places voluntary forage dry-matter intake for adult horses between roughly 1.5% and 2.5% of body weight per day, with 2.0% serving as the ordinary maintenance baseline. The calculator applies that guideline, then does the two conversions most feeding plans skip: correcting for the water still in a bale, and adding an allowance for the hay the horse pulls out of the net and stands on.

How to use the horse hay feed calculator

1. Enter your horse's body weight and pick the matching unit. Without a livestock scale, a weight tape around the heart girth typically lands within about 20 kg, which is close enough for feed planning.
2. Set the feeding rate as a percentage of body weight on a dry-matter basis. Leave it at 2.0% for a horse holding condition in light work, nudge toward 2.5% for a hard keeper or heavy work, or down to 1.5% for an easy keeper or a vet-supervised restricted ration.
3. Enter the hay dry matter. Baled grass or mixed hay is usually 85%–92% dry matter; 88% is a safe default. A forage analysis report gives you the exact figure for your lot.
4. Enter a feeding waste allowance. Slow-feed nets and covered feeders waste roughly 5%; ground feeding or an open round-bale ring can waste 20%–40%.
5. Enter the weight of one bale using the unit on your supplier's tag, since small squares, big squares and rounds differ by an order of magnitude. Weigh one bale yourself if you can.
6. Set the planning period in days and the number of horses sharing this hay, then calculate. Read the daily kilograms as your portion target and the bale count as your purchase order. The chart shows how the ration moves across the 1.5%–2.5% range so you can see a summer and a winter scenario at once.

The forage intake formula, from dry matter to bales

The starting equation computes the daily dry-matter intake from body weight and the feeding rate expressed as a percentage:

Bales are bought as fed, with water still in them, so the dry-matter figure is divided by the dry-matter fraction (also a percentage) to get the as-fed weight :

Hay that hits the floor is bought but never eaten, so the amount you must actually put out is inflated by the waste fraction :

Unit conversion between pounds and kilograms uses the international avoirdupois pound, , applied to both the body weight and the bale weight before anything else happens, so mixed-unit entries stay consistent.

With horses sharing the stack and a bale mass of , the bales consumed per day and across a planning period of days are:

For a sanity check on energy, the calculator also reports the NRC average maintenance digestible energy requirement for an adult horse, which is a linear function of body weight in kilograms:

NRC brackets that average with a minimum-maintenance coefficient of 0.0303 for sedate, easy-keeping individuals and an elevated coefficient of 0.0363 for nervous or highly active ones. Comparing the forage energy your ration supplies against that figure tells you whether hay alone can carry the horse or whether a concentrate is genuinely needed.

Dry matter versus as-fed: the conversion most hay plans miss

Nutrition tables are written on a dry-matter basis because water carries no nutrients and its share swings with weather, cure and storage. Bales, meanwhile, are sold by as-fed weight. Hay baled correctly sits near 12% moisture, which is 88% dry matter; hay baled damp can be 80% dry matter or wetter and is at real risk of mould and spontaneous heating. Weighing out the raw dry-matter number and calling it done underfeeds by about one part in eight, which over a winter is the difference between a horse holding condition and a horse dropping a body condition score.

The correction runs the other way for soaked hay. Soaking to leach water-soluble carbohydrates for a laminitic or insulin-dysregulated horse can drop the dry matter to 30%–40%, so a soaked haynet weighs two to three times the dry hay it started as. Enter the pre-soak dry matter and pre-soak bale weight here, and weigh the net dry rather than dripping.

Feeding waste, and what actually reaches the horse

Published feeding trials put hay waste anywhere between about 1% and 40% depending on the feeder. Small-mesh nets, covered cradles and tombstone-saver rings sit at the low end; hay thrown on the ground, and open round bales in a muddy paddock, sit at the high end. The waste allowance in this calculator inflates the purchase quantity without inflating what the horse eats, which is exactly the right behaviour: your horse still gets its dry-matter target, but your shopping list reflects reality. If you are budgeting hay cost, the waste percentage is usually the single most profitable number on the page to improve.

Worked example: a 500 kg gelding through a 120-day winter

Take a 500 kg gelding in light work, fed at 2.0% of body weight on a dry-matter basis, on grass hay tested at 88% dry matter, fed in a slow net with a 10% waste allowance, from 20 kg small square bales, planned across 120 days.

• Dry-matter intake: 500 × 0.020 = 10.00 kg DM per day (22.05 lb).
• Hay as fed: 10.00 ÷ 0.88 = 11.36 kg per day (25.05 lb).
• Hay offered including waste: 11.36 ÷ 0.90 = 12.63 kg per day (27.84 lb).
• Bales per day: 12.63 ÷ 20 = 0.63 bales.
• Bales for the period: 0.63 × 120 = 75.76 bales, so order 76.
• Total hay to store: 1515.15 kg (3340.34 lb, or 1.52 metric tonnes).
• NRC average maintenance energy: 0.0333 × 500 = 16.65 Mcal DE per day, against roughly 20.00 Mcal supplied by 10.00 kg of dry matter at 2.0 Mcal DE per kg, so forage alone comfortably covers maintenance.

Those are the exact figures the calculator returns for those inputs. Raise the rate to 2.5% for a cold snap and the daily offered weight climbs to 15.78 kg and the 120-day order to 95 bales, which is a 25% larger hay shed and a 25% larger cheque.

Sample scenarios at common feeding rates

The table shows how quickly body weight and feeding rate compound. A 400 kg pony at 2.0% needs about 15 small squares a month; a 600 kg warmblood at 2.5% needs nearly twice that. Those numbers are what make hay the dominant line item in most livery budgets, and why an accurate body weight matters more than any other input here.

Cold weather and the maintenance energy requirement

Below its lower critical temperature a horse spends energy purely on staying warm. For an adult horse with a dry winter coat that threshold sits near 0 °C, ranging from about −15 °C for a well-acclimated, well-conditioned horse out of the wind to around +5 °C for a clipped, thin or wet one. The widely used working figure derived from the NRC maintenance equations is a 2.5% increase in the digestible energy requirement for each 1 °C below that threshold. Forage is the right way to supply it, because hindgut fermentation of fibre generates heat as a by-product in a way that a scoop of grain does not.

The final row is a warning as much as an answer. Voluntary intake tops out somewhere around 2.5%–3.0% of body weight, so a 3.25% requirement cannot be met with hay volume alone. At that point you feed higher-energy forage, add oil or a concentrate, and improve shelter, because the horse physically cannot chew its way to the energy it needs.

Importance of an accurate body weight

Body weight drives medication dosing, trailer load limits and every feed portion on the yard. A livestock scale is the reference method; weight tapes and girth-plus-length formulas are the practical substitutes and carry error of roughly 3%–5%, which on a 500 kg horse is up to 25 kg, or half a kilo of hay a day. Because the error is systematic rather than random, it is worth re-taping monthly and watching the trend rather than trusting any single reading. Track body condition score alongside it: the scale tells you mass, the condition score tells you whether that mass is muscle or fat.

Adjusting intake by body condition score

A horse in heavy work may need more calories than hay alone can carry, and concentrates fill that gap at the cost of raising colic and laminitis risk if fed carelessly. Hay stays the foundation because chewing forage produces the saliva that buffers gastric acid and keeps gut motility steady. Restricting an obese horse below about 1.5% of body weight in dry matter should only be done under veterinary supervision, since prolonged intake below that level risks hyperlipaemia in ponies and donkeys and stereotypic behaviour in any horse.

Hay quality, and why weight alone is not nutrition

Not all hay is equal. Nutrient content varies with species, maturity at harvest, cutting, curing weather and storage. Late-cut hay is stemmy and low in protein; early-cut hay is leafy and dense in energy and protein. Legume hay such as alfalfa runs near 2.2 Mcal DE per kg of dry matter against roughly 1.9–2.0 for mature grass hay, which changes the answer to "is this enough energy" without changing the answer to "is this enough fibre". Mouldy or dusty hay causes respiratory disease and can trigger colic. This calculator weighs hay; only a forage analysis measures it. If you have more than a couple of horses, a lab analysis costs less than a single wasted round bale.

Planning for multiple horses and storage

Enter the herd size directly and the calculator scales the daily requirement and the bale count for the group, which is what you need for an order. If the horses differ widely in weight or workload, run each one separately and add the totals rather than averaging, because the percentage model is linear in weight but your feeding management is not. Storage is the other half of the job: small square hay stacks at roughly 6–8 cubic metres per tonne, so the 1.52 tonnes in the worked example needs about 10 cubic metres of dry, ventilated space, kept off a bare concrete floor on pallets to stop moisture wicking up into the bottom course.

Health implications of getting the ration wrong

Steady forage intake keeps fibre moving through the gut and saliva buffering the stomach. Horses deprived of forage for long stretches develop gastric ulcers, are more prone to colic, and pick up stereotypies such as crib-biting and wood chewing. Overfeeding runs the opposite risk: obesity, insulin dysregulation and laminitis, which is a welfare emergency rather than a cosmetic problem. The calculator gives a defensible starting portion; body condition scoring every two to four weeks tells you whether the number you picked was right for this horse in this season.

Limitations and assumptions: where the percentage model stops working

This tool assumes hay supplies the entire forage intake. In reality it often does not. A horse on good spring pasture might get half its forage from grazing, so the hay number here would nearly double what belongs in the net. The model also treats every kilogram of body weight the same, which breaks at the extremes: an easy-keeping pony holding weight at 1.5% and an event horse burning 2.5% plus concentrates both sit outside the tidy 2.0% default. It assumes a constant dry matter across the whole lot, whereas bales from the top and bottom of a stack can differ by several percentage points. It uses simple calendar days with no allowance for hay lost to spoilage in storage, which on outdoor-stored round bales can be another 10%–25% on top of the feeding waste figure.

Metabolic conditions rewrite the rules entirely. A horse with equine metabolic syndrome, insulin dysregulation or PPID usually needs hay tested for non-structural carbohydrates and often soaked to strip sugar, not simply weighed out. Late-pregnant and lactating mares, growing foals and senior horses with worn teeth all deviate from a flat percentage of body weight, and NRC gives them separate equations that this page does not implement. The maintenance energy figure reported here is the average coefficient and says nothing about protein, calcium, phosphorus, trace minerals or vitamin E, all of which forage-only diets commonly fall short on. Treat the output as a purchasing estimate and a starting portion, then let your veterinarian or an equine nutritionist tune it against body condition, a forage analysis and any diagnosed condition.

Hay Loft Winter: the planning game on this page

Below the calculator is Hay Loft Winter, a barn-loft simulation that runs the same arithmetic under time pressure. You stock the loft with a chosen bale type and count, then a winter season plays out day by day. Each day the herd's dry-matter requirement is recomputed from the temperature using the same 2.5%-per-degree cold uplift described above, the stack of bales visibly shrinks, and each horse's body condition score drifts up or down depending on whether the ration you set covers its need. Run out of hay and condition collapses; overfeed and the horses tip past a body condition score of 7. It is the fastest way to feel why the dry-matter and waste corrections matter: guess the stack size from the as-fed bale weight alone and you will be short before the thaw.

Turning the numbers into a feeding routine

The daily kilogram figure is the one to internalise, because it becomes a weighed haynet or a countable number of flakes. Weigh a full net on a luggage or fishing scale once so you know what the target portion looks like, and you rarely need the calculator again for that horse until its weight or workload changes. The bale count is the other half: it tells you how much to order and how much dry, ventilated storage to keep clear so the hay does not spoil before it is eaten. Use the copy button to drop the summary into a stable log or budget spreadsheet.

Run the numbers at least twice a year: once heading into winter when pasture dies back and hay carries the whole diet, and once in spring when grazing returns and the ration can come back down. Between those checks, let ribs, topline and energy tell you whether the percentage you picked is holding. Explore related planning tools such as the Hay Bale Yield Calculator, the Pasture Stocking Rate Calculator, and the Tractor PTO Horsepower Calculator to coordinate forage production, grazing pressure and equipment needs.

Frequently asked questions about horse hay requirements

Sources and further reading

Sources: the 1.5%–2.5% of body weight forage dry-matter guideline, the 2.0% maintenance baseline, the maintenance digestible energy coefficients (0.0303, 0.0333 and 0.0363 Mcal per kg body weight per day) and the dry-matter basis for all intake figures follow the National Research Council, Nutrient Requirements of Horses, 6th revised edition (2007), National Academies Press. The cold-weather uplift of about 2.5% in digestible energy per 1 °C below the lower critical temperature is the standard extension interpretation of the same NRC maintenance model. Body condition guidance follows the Henneke 1–9 scoring system (Henneke, Potter, Kreider and Yeates, 1983, Equine Veterinary Journal 15(4):371–372). Pound-to-kilogram conversion uses the international avoirdupois pound, 1 lb = 0.45359237 kg. Adjust for pasture intake, a laboratory forage analysis and any diagnosed metabolic condition with your veterinarian or an equine nutritionist.