Mike - If you keep careful records of what comes in from the field, you can get a dollar value and/or pound value to determine how many share equivalents (SE) you are producing. This may not be what you are considering, but it is a postmodern approach (try to sell as much as you can grow rather than the modernist marketing approach of growing what you can sell). For example, in 2013, I have produced $12,575 worth of food on .52 acres so far at $550 per share for an SE of 23. Since the season is not finished yet, an SE of 25 per half acre or 50 per acre is a good approximation. You will find 40 shares per acre quite common in anecdotal evidence and that was my measure in 2012 and 2011. My current research is into small-scale efficiency and it seems to be working. For example, producing my own bean and corn seed allows me to slack off on weeding because I concentrate on varieties that need less labor-intensive practices.
Disclaimer: These numbers do not reflect what I actually sell, but only what I produced. In your case, I assume you have multiple markets, but if you can analyze your production, it will tell you what your farm is capable of.