Here's a sentence from a proposal for a Dallas project,which is supposed to be "economically, environmentally and socially sustainable": "Some of the unusual features to be included in the 2.5 acre block include enough garden space to feed around 300 inhabitants, 40% affordable housing, an educational element that serves all of the residents and fully renewable, off-the-grid energy." That's roughly 350 square feet per person. Not sure how you do much meat off that area, so presumably these are 300 vegans. And I personally doubt the ability of 350 square feet to provide all the fruits and vegetables for a person, much less the grain.
[Some may say I'm willfully misreading the description, that "sustainable" doesn't mean self-sufficient. That may be true, but still a reasonable modesty in claims would be fitting.)