There's 900 million acres of farmland in the US, producing plant-based food, but also raising livestock for meat (which makes up a majority of the farmland). The US exports about 20% of their food production, and imports a similar amount, so we'll just call it even (it's literally an apples to orange comparison anyhow, since the imports are things like fruit and liquor, while exports are mainly grain and meat). With a population 330 million, that means that the average American is eating food grown and raised on ~2.5 acres of land.
In other units: in the current American system of food production, you can feed 250 people on 1km^2 of land. Let's use Chicago as our example city, with a population of ~10 million people. They are eating food that is grown and raised on 25 million acres of land, or 100,000 km^2. That's about 2/3rds of the land in the state it resides in, Illinois. Illinois itself is only ~12 million people, so you could basically think of Illinois "carrying capacity" as being 15 million people.
This analysis is very different if you use other countries as a basis. China and India have a lot less overall useful farmland, and it's been farmed much longer, with more labor, and with less mechanization. It ends up being more productive in terms of calories per acre, but with less worker productivity.
It is also worth noting that of that 900 million acres, only a portion of it goes towards food for humans or livestock. Most of the corn and soybeans grown are used industrially for ethanol, lubricants, acids, starches, and rubber. We also grow things like tobacco, medicines, and cotton, which may be needed, but are not food. A significant portion of corn is also traded as a currency "commodity crop" in a market I don't understand at all.
If I recall correctly, roughly 40% of farmland is dedicated to food production for livestock, and 2% is dedicated to food for direct human consumption. So assuming you already have all necessities, and only need food without any change to an average american diet, we may need as little as 1.05 acres per person, following your math.
Some back-of-the-envelope math:
There's 900 million acres of farmland in the US, producing plant-based food, but also raising livestock for meat (which makes up a majority of the farmland). The US exports about 20% of their food production, and imports a similar amount, so we'll just call it even (it's literally an apples to orange comparison anyhow, since the imports are things like fruit and liquor, while exports are mainly grain and meat). With a population 330 million, that means that the average American is eating food grown and raised on ~2.5 acres of land.
In other units: in the current American system of food production, you can feed 250 people on 1km^2 of land. Let's use Chicago as our example city, with a population of ~10 million people. They are eating food that is grown and raised on 25 million acres of land, or 100,000 km^2. That's about 2/3rds of the land in the state it resides in, Illinois. Illinois itself is only ~12 million people, so you could basically think of Illinois "carrying capacity" as being 15 million people.
This analysis is very different if you use other countries as a basis. China and India have a lot less overall useful farmland, and it's been farmed much longer, with more labor, and with less mechanization. It ends up being more productive in terms of calories per acre, but with less worker productivity.
It is also worth noting that of that 900 million acres, only a portion of it goes towards food for humans or livestock. Most of the corn and soybeans grown are used industrially for ethanol, lubricants, acids, starches, and rubber. We also grow things like tobacco, medicines, and cotton, which may be needed, but are not food. A significant portion of corn is also traded as a currency "commodity crop" in a market I don't understand at all.
If I recall correctly, roughly 40% of farmland is dedicated to food production for livestock, and 2% is dedicated to food for direct human consumption. So assuming you already have all necessities, and only need food without any change to an average american diet, we may need as little as 1.05 acres per person, following your math.