I've seen a few questions about how much hay one should they feed their horse per day. So after much research, including but not limited to speaking with nutrition specialists, vets & even a farrier or 2, I will break it down & make it as simple as possible & I will include how much hay you would need for 31 days. I pushed these findings all to 31 calendar days even though there is 28 during a leap year & 30 days in some months.

For any horse the bare minimum forage requirement per day is 1% of their body weight. This meets the daily intake requirements a horse needs in forage. * I would like to note that I am not a hay specialist. If you need further information, please contact your Vet, Hay supplier or an Equine Nutritionist. They can better help you with particulars of each hay or legume. 

Not all hay is created equal & this should be taken into consideration when it comes to vitamins & minerals as well as weight of the hay itself. 

I would suggest weighing your hay each time you feed until you get a good idea of just how much you should be feeding at each meal. It can be time consuming, but until you are comfortable with how much each feeding should weigh, you could be feeding too little or too much depending on how much your horse should weigh. Going into winter, you would feed more because they use more energy to keep warm & less going into spring because they won't be using that extra feed. Plus spring grass will be coming up for most folks across the U.S. & if you turn your horse out to pasture, you won't need as much hay. 

Horses in nature graze 6 hours or more per day. I don't believe anyone would put out enough hay for their horse to graze on for that length of time. Some horses rapidly consume their hay while others it would take a lot longer  to consume that amount. This chart will break feeding down to 3 times per day. Or if you prefer you can figure out how much each serving should weigh & feed accordingly.

For a 900lb horse:

1. 1% body weight = 9lbs hay per day, 3lbs per feeding x 31dys=279lbs hay
2. 1.5% body weight = 13.5lbs hay per day, 4.5lbs per feeding x 31dys=418lbs hay
3. 2% body weight = 18lbs hay per day, 6lbs per feeding x 31dys=558lbs hay
4. 3% body weight = 27lbs hay per day, 9lbs per feeding x 31dys=837lbs hay

For a 1000lbs horse:

1. 1% bdy wt = 10lbs hay per day, 3.3lbs hay per feeding x 31 dys=310lbs hay
2. 1.5% bdy wt =15lbs hay per day, 5lbs hay per feeding x 31dys=465lbs hay
3. 2% bdy wt = 20lbs hay per day, 6.6lbs hay per feeding x 31dys=620lbs hay
4. 3% bdy wt = 30lbs hay per day, 10lbs hay per feeding x 31dys=930lbs hay        

For a 1100lb horse:

1. 1% bdy wt = 11lbs hay per day, 3.6lbs hay per feeding x 31dys=341lbs hay
2. 1.5% bdy wt = 16.5lbs hay per day, 5.5lbs hay per feeding x 31dys=511.5 hay
3. 2% bdy wt = 22lbs hay per day, 7.3lbs hay per feeding x 31dys=682lbs hay
4. 3% bdy wt = 33lbs hay per day, 11lbs hay per feeding x 31dys=1023lbs hay  

These are average weights of horses & as you can see, the more you feed per day, the more you'll need for a month's time for just 1 horse. As I stated in the beginning 1% is the bare bones minimum for a horse. If your horse is a pasture ornament, is never exercised or ridden at any time, it may do well with just 1% of hay however it won't be putting on any weight for the winter months unless it has pasture to graze on daily or you feed supplemental forage such as pelleted or cubed feeds, grains or beet pulp. 

For those of you who ride or exercise your horse daily, the energy expelled by your horse is much greater & therefore will require more feed to keep on weight. Most of the nutrition experts say that the best way to keep your horse healthy is by feeding quality hay, such as an Alfalfa mix, Timothy mix, or a high quality Orchard mix. The hay should be green, smell fresh & be free of weeds & bugs. Don't ever feed questionable hay to your horse. If it's moldy or has a lot of dirt-dust in it don't feed it. Horses can get colic quickly from moldy hay. 

My personal experience, I buy a round bale from my local hay supplier each month. Cookie gets 2-3% daily or roughly 6-8lbs of hay per feeding per day, plus 2lbs of wetted Alfalfa cubes with 2 teaspoons of milled flax seed twice a day & 1 teaspoon of ground up mineral block once a day. The reason for the low amount of mineral block is because she has free access to her white salt lick & won't lick the mineral block. This way she doesn't get an over abundance of salt, but does get extra minerals & it uses up the block without wasting it. Also, Cookie gets worked 5 days a week for 30-45 minutes (longer if the weather is nice). I want her to stay on her weight gain, so I feed her more hay for progress. 

I hope this chart helps you to figure out how much your horse should be getting each day in forage & to see how much hay you'll need for a whole month.