There are no hard and fast rules about how much hay you can produce on one acre, but the more nutrients your soil has, the more hay you should be able to produce. The most important thing to remember is that the quality of your forage is limited by the quantity of nutrients available in your soil.
An average yield of hay per acre is  somewhere between 1 and 2 tons per cutting. Some grasses can yield much more, but this is usually the result of an exceptionally good growing season. The most important factor in a high yield is a good growth cycle. The growing season should be long enough so that all the plants have time to mature. A long growth cycle is best achieved by early planting and late harvesting.