Is there a rule of thumb regarding number of horses per acre?

You should always check with the local county officials in charge of land use in your area. Generally speaking, if local requirements allow, one and a half acres of property per horse is considered ideal. This number pertains to the property size as a whole, assuming you will be using the entire property as a horse facility with house, barn garages, etc. If this seems like a lot, keep in mind that this figure takes into account not only sufficient grazing area, but maintenance as well. The amount of upkeep on your land can be substantial, depending upon where you live. If you live in a dry climate, the horses tend to not tear up the ground quite so badly, but suitable forage grass may be scarce. Conversely, a wet climate becomes quite muddy and grass gets destroyed by heavy traffic, but adequate forage is usually not a problem due to favorable growing conditions. 

The acre and a half rule seems to have developed over time through trial and error, based upon the experiences of horse people around the world. With this approach it seems that access roads hold up longer, fences need repair less often, pastures can be managed realistically, and overall maintenance does not become a runaway train. Of course, many facilities do not have this option, and have to make things work with what they have. If during the planning stage there is a choice, however, then an acre and a half per horse usually results in happier horses and people.

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