Figure out exactly how much barn or shed space you need to store hay for your herd — by livestock type, months of storage, and bale size — so you don't run short mid-winter or waste money on a barn that's too big.
Buying hay in summer and storing it yourself almost always saves money versus buying in winter when prices spike. But only if you have enough dry, ventilated storage — improperly stored hay molds, loses nutrition, and in worst cases causes spontaneous combustion. Knowing exactly how much space you need is the first step.
Hay storage is one of those things every livestock owner underestimates when they start out. The numbers seem manageable until you're staring at 200 small square bales trying to fit them into a 12x12 shed. Getting the math right before you build (or buy) a storage structure saves money and protects your feed investment.
When in doubt, build or rent 20–30% more storage than your calculations suggest. Hay quality varies year to year, and having extra capacity lets you buy when prices are low.
A 10x20 foot shed is 200 sqft. At an 8-foot stack height, usable volume is 1,600 cubic feet. Small square bales are roughly 0.875 cu ft each when stacked tight. Theoretically that's around 1,800 bales — but realistically you need working room and airflow, so expect to fit 600–900 bales comfortably.
A 1,000-lb horse on hay-only feeding eats roughly 1.5–2% of its body weight per day in hay — about 15–20 lbs per day, or 5,000–7,000 lbs per year. That's 100–140 small square bales per horse, or 5–7 tons. Add 20% for waste and feeding losses.
Round bales can be stored outside with net wrap or a tarp, though expect 15–30% loss to weathering versus 5% or less in a dry barn. Small square bales fare much worse outside — they absorb moisture and mold quickly. Always try to keep small squares under cover. A basic 3-sided pole barn is far better than full outdoor storage.
Bad hay smells musty or dusty, feels slimy, has visible mold (white, gray, or black), is unusually hot to the touch, or has an ammonia smell. Animals will often refuse moldy hay. Dusty hay causes respiratory problems (heaves in horses). When in doubt, toss it — the cost of sick animals far exceeds the cost of bad hay.
Stack on pallets or lumber to keep off concrete, with the cut side up (not the strings) to allow airflow. Leave 6–12 inches between the wall and the hay stack for ventilation. Stack in a crosshatch pattern for stability over 4 bales high. Orient bales so they can be pulled from the front — first in, last out is fine for hay as long as the bales were dry when stored.