How much hay do you need for the winter?

What the number means

The tons that come out are the hay you must have in the barn on the first day of feeding, not the hay the animals eat. Animals eat a share of their body weight in dry matter every day; the hay carries some water; part of what you put out is trampled, soiled or left; and part of what you store spoils before you feed it. The calculator follows the hay through all four steps and shows how much is lost at each one, so you can see what a rack or a roof is worth.

The formula

Dry matter eaten (lb) = animals × weight × intake share × days. Hay eaten = dry matter ÷ the hay’s dry matter share. Hay put out = hay eaten ÷ (1 − feeding loss). Hay to have = hay put out ÷ (1 − storage loss). The two losses are divided out rather than added, because each is a share of what was there before the loss. Tons are short tons of 2,000 pounds, bales are the total rounded up, and the cost is tons times your price. An animal unit is 1,000 pounds of body weight, the same unit as in the stocking rate calculator; the table prints how many your animals make.

Worked example from Mississippi State

Mississippi State Extension publication P2540 works a herd of 30 cows of 1,200 pounds, each eating 2 percent of its body weight for 180 days, with hay at 85 percent dry matter. The cows eat 30 × 1,200 × 0.02 × 180 = 129,600 pounds, 64.8 tons, of dry matter. Divided by 0.85 that is 76.2 tons of hay. Stored in a barn with a 5 percent loss the herd needs 80.2 tons, and left outside on the ground with a 35 percent loss 117.3 tons, the 117 tons of the publication: 37 tons more for the same cows, simply because of where the bales sat. (The publication prints 77 tons for the barn case, from 76 ÷ 0.95; the quotient is 80.2.) The default numbers in the calculator are a smaller case: four 1,000-pound horses, 150 days, large bales in a rack. They need 7.8 tons, 16 bales of 1,000 pounds and, at $100 a ton, $781.

Limits of the method

The losses are averages from particular trials. The Missouri table is for beef cattle, and a rack that holds waste to about 5 percent for cattle is not guaranteed to do the same for other animals. The storage ranges are wide for the same reason: Mississippi State’s own table runs from 5 to 20 percent for exposed bales on the ground in the first nine months and to 35 percent or more after 12 to 18 months, and quality is lost on top of the weight. Hay quality is not in the formula either: a poorer hay may need to be fed at a higher rate, and Alabama Extension notes that the nutrient content of a forage can only be known by testing. Finally, intake varies by animal: Alabama Extension notes that some horses eat more than 3 percent of their body weight. Treat the result as a planning figure and add a margin if a long winter would be costly.

How much hay does a horse eat in a winter?

Alabama Extension recommends about 2 percent of body weight a day in dry matter, which is 20 pounds for a 1,000-pound horse, and says that horses allowed to eat as much as they want will take 2 to 2.5 percent. At 90 percent dry matter, a 1,000-pound horse needs about 22.2 pounds of hay as fed a day, 667 pounds in 30 days, or 14 fifty-pound square bales a month before waste. Over a 150-day winter that is 1.7 tons per horse before any loss.

How many bales do I need for the winter?

Divide the tons you need by the weight of your bale. Four 1,000-pound horses for 150 days at 2 percent, with hay at 85 percent dry matter, a 5 percent storage loss and large bales fed daily from a rack (4.9 percent loss), need 7.8 tons, which is 16 bales of 1,000 pounds. The weight of a bale depends on its size, density and the hay, so weigh a few of yours: Mississippi State's example is a 5 × 4 foot bermudagrass bale of 1,000 pounds, and the Alabama tables use 50-pound square bales.

How much hay is wasted in feeding?

It depends mostly on how it is fed. In the University of Missouri table, large bales in a rack lose 4.9 percent when fed daily and 5.4 percent as a seven-day supply. Without a rack the loss is 12.3 percent when fed daily and 43 percent when a seven-day supply is left out. Small square bales lose 3.9 percent in a rack and 6.7 percent without one. Missouri also says unrolled or processed bales left for three days or longer lose 40 percent or more, against about 12 percent when fed daily. For the four horses above, 43 percent loss instead of 4.9 percent raises the purchase from 7.8 to 13 tons. Those figures were measured on beef cattle; horses and other stock waste differently.

How much hay is lost in storage?

Mississippi State Extension, using Oklahoma State data, gives dry matter losses of 5 to 20 percent for round bales stored on the ground and exposed for up to 9 months and 20 to 35 percent or more after 12 to 18 months. Bales on pallets or tires under cover lose 2 to 4 percent, bales under a roof 2 to 5 percent, and hay kept in an enclosed barn is reported at more than 2 percent for up to 9 months. The storage field takes the percentage you choose.

Is it 2 percent or 3 percent of body weight?

Both are used, for different animals and kinds of hay. Mississippi State's cattle example uses 2 percent of body weight in dry matter, and Alabama Extension gives 2 percent as a horse's target with 2 to 2.5 as free choice, noting that some horses eat more than 3. Nebraska Extension's 26 pounds of forage per 1,000-pound animal unit per day works out to 2.6 percent. The field is open so that you can use the number your veterinarian, nutritionist or extension agent gives you.

What percent dry matter is hay?

Mississippi State's example uses 85 percent, and Alabama Extension says hay is approximately 90 percent dry matter. A test of your own hay gives the real value, which matters because the animals eat dry matter and you buy water too. Going from 90 to 85 percent adds about 6 percent to the hay you need.

Sources: Mississippi State University Extension, P2540 “Hay Storage: Dry Matter Losses and Quality Changes” (R. Lemus; Table 2 after R. Huhnke, Oklahoma State, 2003; worked example of 30 cows); University of Missouri Extension, G4570 “Reducing Losses When Feeding Hay to Beef Cattle” (R. Kallenbach, September 2017; Table 1 and text on unrolled bales); Alabama Cooperative Extension System, ANR-3153 “Estimating & Supplying Equine Forage Requirements” (C. Heaton, Auburn University); University of Nebraska–Lincoln Extension, NebGuide G2344 (animal unit and 26 pounds per day), all read October 28, 2026. The price shown is only an example. Related: horse weight calculator, stocking rate calculator for the grazing months, chicken coop size calculator and fence calculator. How we check our calculators.