My family of four lives in a 800 sq/ft apartment, and it’s mostly big enough for us. Makes me wonder: If 200 square feet per person is all anyone really needs, then shouldn’t we be able build a house big enough for everyone? 200 sq/ft x 7B = 1.4T sq/ft. 1.4T squared =~1.2 million feet per side. Why, that’s a building only ~ 230 miles per side! If we built the apartment 10 stories high, would we really be able to house all of humanity in a building 23 miles square?
A related question: What if were to take every person and put them into individual boxes, say 2x3x6 feet, and made a cube from all the coffins, er - boxes, how big a block would we have?
Sorry I lack the math skills to decipher this myself. Being more right-brained, I went into nursing instead. (Spooky what we nurses think about during night shift, huh?)
It’s really only a function of how much space you want to allocate to each body, and you might as well stack them like wood because they can’t live in such a place. They need space for the millions of businesses that provide food, transportation, security, education, basic services etc. I would imagine the infrastructure required for transportation just to get a few billion people in and out of this building to go to work every day would make it impossible.
You personally need (for physical and mental health) and use more space than what’s inside your house, even before taking into account the industries and infrastructure that Fubaya mentions.