How this hay calculator works
Extension intake tables are published on a dry-matter basis — a dry beef cow on average-quality forage eats about 2.2% of body weight in dry matter per day (Oklahoma State: 1.8% on low-quality forage up to 2.5% on high-quality). But hay isn't pure dry matter: it's typically ~88% DM. Our ruminant presets already do that conversion for you — e.g., the beef-cow preset shows 2.5% because 2.2% DM ÷ 0.88 ≈ 2.5% as-fed hay, which is what you actually buy and feed. The horse preset uses the University of Maryland's as-fed rule directly (a 1,000-lb mature maintenance horse eats about 20 lb of hay a day). The formula:
Total hay (as-fed) = weight × as-fed intake% × head count × days ÷ (1 − waste)
Waste is a combined storage + feeding loss and matters more than most people expect: a typical unrestricted ring feeder can run ~25%, ground feeding worse, and limiting access to a feeder can bring it near 10%. If your winters run long, add two to four weeks of cushion — hay is cheaper in September than in February.
Typical daily hay intake (as-fed, presets)
| Animal | Typical weight | As-fed intake (% BW) | Hay per day |
|---|---|---|---|
| Horse (maintenance) | 1,000 lb | 2.0% | ~20 lb |
| Beef cow (dry) | 1,300 lb | 2.5% (≈2.2% DM) | ~33 lb |
| Dairy cow (dry) | 1,400 lb | 2.3% (≈2.0% DM) | ~32 lb |
| Goat | 150 lb | 3.4% (≈3.0% DM) | ~5 lb |
| Sheep (ewe) | 175 lb | 3.4% (≈3.0% DM) | ~6 lb |
Growing, late-gestation, and lactating animals need more — sometimes much more. Lactating dairy cows in particular need a balanced ration, not a hay rule of thumb; work with your nutritionist. Forage quality shifts intake up or down.
Dry matter and as-fed are not the same number
This is the first place a hay budget goes wrong, and it goes wrong quietly. Nutritionists work in dry matter because that is the only basis on which two feeds can be compared — the water in a feedstuff carries no energy and no protein, so a requirement expressed in pounds of dry matter stays true whether the animal is eating hay, silage or standing grass. Extension intake tables inherit that convention.
What you buy, haul and throw over the fence is not dry matter. Cured hay carries roughly 12% moisture, so about 88% of the weight on the scale is actually feed. If you take a dry-matter percentage straight off a table and apply it to as-fed hay, you under-buy by about that same 12% — not enough to notice in a week, but close to three weeks of feed missing from a 150-day winter. The presets on this page have already been divided out for you, which is why the beef-cow preset reads 2.5% rather than the 2.2% you may have seen quoted. If you type your own number into the intake box, make sure you know which basis it came from.
The correction runs the other direction for wet hay. A bale put up damp weighs more per bale but delivers less feed per pound, so the seller is paid for water and the animals are shorted. That is a quality and storage problem before it is an arithmetic one, but it shows up here too.
The arithmetic mistake almost everyone makes with waste
Waste gets added by multiplying, and it should be added by dividing. The difference sounds pedantic and is not.
If a cow eats 4,875 lbs over the winter and you expect to lose 15% of what you put out, buying 4,875 × 1.15 = 5,606 lbs is wrong. That figure is 15% more than what she eats — but the 15% you lose comes out of what you buy, not out of what she eats. The correct move is 4,875 ÷ 0.85 = 5,735 lbs, and the calculator above does it that way. At 15% the gap is only about 130 lbs, so nobody notices. At the 35% unrolled-bale setting the same consumption figure gives 4,875 ÷ 0.65 = 7,500 lbs the right way and 6,581 lbs the wrong way — a shortfall of over 900 lbs, which on 700-lb bales is more than a full bale per cow. In a twenty-cow herd, that is a semi load you did not buy.
The second common error is subtler: people budget for the animals and forget the arithmetic runs on average weight. A herd of 1,200-lb cows with three 1,700-lb bulls and a set of weaned calves is not well described by one number. Split unlike groups and run them separately, then add the totals.
A worked example, start to finish
Take the page defaults: two mature horses averaging 1,000 lbs, fed for 150 days, at 2.0% of body weight as fed, with a well-managed ring or rack feeder at 15% loss, on 4×5 rounds assumed at 700 lbs.
Two things in that example are worth staring at. The first is the rounding: 10.08 bales becomes 11, because you cannot buy a tenth of a bale and running out in March is not a rounding error you can absorb. The monthly figure rounds up the same way, so twelve monthly numbers will not add to the seasonal total — use the total.
The second is how much of the answer lives in the bale weight. Those same 7,059 lbs are 11 bales at 700 lbs and 6 bales at 1,300 lbs. Both are round bales. If you agreed on a price per bale without agreeing on a weight, you have not actually agreed on a price.
How to measure honestly
Three inputs deserve real measurement rather than a guess, and they are not the three people usually check.
Bale weight is first. Weigh a loaded trailer and then the empty trailer at any truck scale, co-op, grain elevator or landfill scale and divide by the bale count — that single trip removes the largest uncertainty on this page. Weigh bales from the field you are actually buying from, because density varies with the baler operator, the twine or net tension, and the moisture at baling. Weighing one bale is far better than none; weighing five and averaging is better still, since bales off the same wagon commonly differ by more than people expect.
Animal weight is second. Most people underestimate mature cattle and overestimate horses. If you have no scale, a weight tape gets a horse within a usable range, and a livestock scale at the sale barn or vet clinic settles cattle. A 200-lb error on a cow is a 200-lb error compounded across every feeding day in your season.
Feeding days is third and is usually the sloppiest. Count from the day pasture stops supplying real feed to the day it starts again — not first frost to last frost, which is a different and shorter interval. Your own records from previous winters beat any regional average, because they include your ground, your species mix and your tolerance for feeding early. If you have no records, start from the 120–180 day range in the input hint and lean long.
What this calculator cannot tell you
It cannot tell you whether the hay is any good. Quantity and quality are separate questions, and this page answers only the first. Two bales of identical weight can differ enormously in energy and protein depending on species, maturity at cutting, weathering and storage, and an animal fed all it wants of poor hay can still lose condition. A forage test from a lab is the only way to know, and it is the input a ration is actually built from.
It cannot tell you whether hay alone meets the requirement. Growing animals, late-gestation females and anything lactating need more than a maintenance rule of thumb provides, and often need supplement rather than simply more hay. Lactating dairy cattle in particular need a balanced ration from someone who has seen your forage test.
It cannot see storage losses that happen before feeding. Bales stored outside on the ground in a wet climate lose a share of their weight to weathering and spoilage that never reaches an animal's mouth, and the waste selector is a combined figure that assumes ordinary handling, not a bad situation. It also cannot see mud, wind, bedding use, or hay pulled out and slept on.
And it cannot price anything. For what hay is actually trading at, and for converting a per-ton quote into a per-bale quote before you agree to it, see hay prices by state. That converter is the companion to this one: a $180/ton quote on a 700-lb bale is $63/bale, and a seller quoting per bale without a weight is quoting nothing at all.
When the answer changes
Cold is the big one. Below a horse's lower critical temperature — around 18°F for a horse in good winter coat, per University of Minnesota guidance — energy needs rise roughly 1% for each additional degree of drop, and wind, rain and lack of shelter move that threshold upward. Cattle follow the same pattern. A two-week cold snap does not change your seasonal total much; a cold winter changes it a lot, and the extra feed has to come from somewhere.
Forage quality changes it in both directions. Oklahoma State's range runs from 1.8% of body weight on low-quality forage to 2.5% on high-quality, because animals physically cannot eat enough of a coarse, mature, slow-digesting hay to meet requirements — intake falls exactly when the feed is worst. Good hay gets eaten faster and disappears sooner, which surprises people who switch suppliers mid-winter.
Feeder changes it. The gap between the 10% and 35% settings on this page is over three times the loss, and the equipment that closes that gap generally pays for itself inside a season or two at any hay price worth mentioning.
And the calendar changes it. A late spring extends the feeding period at the expensive end, which is why the calculator's tip suggests two to four weeks of buffer. Hay bought in September and not needed is still hay next year. Hay needed in March and not bought is bought at March prices.
Frequently asked questions
How much hay does a horse eat per day? About 2% of body weight — 20 lbs a day for a 1,000-lb horse, roughly 600 lbs a month, before waste.
How many round bales for one cow for winter? A 1,300-lb dry beef cow at ~2.2% of body weight in dry matter (≈2.5% as-fed) for 150 days eats about 4,900 lbs of hay; with 15% waste you should plan to buy roughly 5,700 lbs — 8 to 9 typical 700-lb 4×5 round bales.
Should I feed more hay when it's cold? Yes, and it's species-specific. For horses, University of Minnesota guidance: below a horse's lower critical temperature (~18°F for a winter-coated horse), energy needs rise about 1% for each additional °F drop — wind, wetness, shelter, and body condition move that threshold. Cattle guidance is similar in spirit. In a hard winter, the safest plan is extra hay on hand.
Sources
- University of Maryland Extension — Calculating Your Horse's Winter Hay Needs
- Oklahoma State University Extension — Nutrient Requirements of Beef Cattle (dry-matter intake by forage quality; bale weights)
- University of Minnesota Extension — Efficiently Feeding Hay to Cattle; Caring for Your Horse in Winter
- NC State & Penn State Extension — winter hay planning guides