The number of acres a person needs to have for a horse varies greatly. Local ordinances can limit the number of horses by acre or ability to take care of the animal.
When trying to determine how much acreage is needed to own a horse, there are two things to check out. First, contact the local municipality to find out more about ordinances. The municipality will almost certainly have a limit on how many horses one person or organization can own. The limit may likely be based on the acreage available to the animals. Some municipalities may also have other requirements for horse ownership based on whether or not the horses will be in paddocks, what kind of food they will receive or if they are to graze for food, and even how drainage is set up.
The second item to consider is if the amount of land owned is really enough to support a horse. Most horse owners expect their animals to graze for much of their food. If the land is not large enough to support a grazing animal or even if it is barren, this may be a problem. Some horse owners and farmers have to calculate how many animals their soil can support based on its quality, as stated by the United States Department of Agriculture's Natural Resources Conservation Service.