100% this is correct. We have 10 raised beds that are 4'x16', and we supply probably 1/2 of what we need for the year for a family of 3. We're super efficient and good at this, too.
The normal estimate is that it takes 1 acre of land to feed a person for the full year. One acre is 43560 square feet. Your 10 beds are 640 square feet.
Somewhere the math is very very wrong.
Your estimates are based on what, grain production? That grain production equals meat and other things, not just produce. That estimate is also based on traditional row-cropping, is my guess.
Also, at the heart of it, your impression is incorrect. I didn't say the raised beds provided 50% of the family's calories, but 50% of our vegetable and other fresh produce needs. This does not include meat, most proteins in general, or fruits.
Finally, it is an assumption comparing traditional row cropping to square foot gardening in the raised beds. You get much more produce in a smaller space in square foot versus row crops, but it is much more labor intensive. You cannot use machinery in square foot gardens, compared to row crops. So there is a trade off.
In other words, the math doesn't work with your assumptions, because they're two different things. My estimate is that, while the garden produces 50% of our vegetable and produce needs, it's probably 10-20% of our overall caloric consumption. But that's a madey upey number, really. I have no idea.
1 acre/person is roughly what a pre-mechanization, pre-chemical-fertilizer, pre-pesticide subsistence peasant needs to keep himself alive.
https://www.growveg.com/guides/growing-enough-food-to-feed-a...
> with about another 4000 square feet (370 square meters) for access paths and storage
https://www.wolframalpha.com/input/?i=arable+land+usa+in+acr...
https://www.wolframalpha.com/input/?i=arable+land+europe+in+...
Basically with that rule of thumb USA is on the verge of starvation and EU has been starving for a few decades already.
And this doesn't even consider the fact that eating animals is less efficient than eating plants. Where is the food for the 8 billion chicken and 70 million pigs in the USA coming from?
From my own calculations roughly 3588 sqft of wheat are necessary to feed a single person. Of course people are different, farms are different and plants are different. So a rule of thumb of 4000 sqft sounds about right and matches DoreenMichele's number.
That is not an estimate, it is a meme.