To estimate how much hay to buy for the winter, you can run a few simple
calculations. We will assume that horses (other livestock species vary slightly
in daily consumption rates, but calculation would be similar) eat approximately
2-2.5% of their body weight in hay per day as their full ration. If your horses
have higher energy needs and also receive grain meals, you can subtract the
weight of grain from the 2% figure based on your horse's weight. We will also
assume that the hay season lasts from November to March, and that horses
have high-quality pasture for forage during the rest of the year.

1 horse at 1100 pounds x 2% BW = 22 lbs hay per day (if you feed grain,
subtract its weight from this number)

22 lbs x 150 days = 3300 lbs hay per horse

Don't forget to account for wastage! Here, we will assume 5% storage waste
because our bales are stored inside and 13% waste from feeding small
square bales on the ground (No feeder: 13%, Hay rack: 5%, Basket feeder:
3%.)

3300 lbs x 1.05 (storage waste) x 1.13 (ground waste) = 3915 lbs hay per
horse

If you buy your hay by the ton, this would be 3915/2000 = almost 2 tons of hay
per horse.

If you buy your hay by the bale, you will need to find out the approximate
weight of each bale. Assuming a 40 lb bale, 3915/40 = 98 bales per horse.