To cover 100% of your food needs? About 200 square feet per person.
If you’ve only ever gardened for fun, or to supplement your store-bought groceries with some tasty home-grown treats, you might not be aware of just how much space is required to feed someone. You may have noticed that family farms are kind of large, and there’s a very good reason for that (though some of that space was traditionally given over to livestock and draft animals). Estimates vary. Different crops require different amounts of space, for example, and some gardening gurus estimate you’d need at least 4,000 square feet per person, with more space allotted for stuff like lanes between crops.
Most of us don’t have 4,000 square feet to dedicate to gardening, but you probably don’t need quite that much as long as you’re efficient. A good rule of thumb is that you need about 200 square feet per person for a self-sustaining garden. So if you’re a family of four, figure you’ll need about 800 square feet, or a space about 20x40 or 10x80.
That’s ... still a lot of space, especially if you’re in an urban setting. The key is planning your garden out, because different crops take up different amounts of space, and if you’re going to live off of those crops you have to include a wide variety of plants for nutritional completeness. Your garden will need to include these: