This can be a surprisingly difficult thing to measure, for a little surprising reason:

The city with most floor space per person is among the cities with the lowest population density. It will be a city where the maximum amount of homes are detached houses. And probably one where the "urban" planning is less dense than in your standard suburbia.

It will be a very small city by population.

And that leads us to the problem: how do we define "city"?

There are several competing definitions for what constitutes a city, and since we're talking about cities at the very lowest end of the population scale, you'll get a big pile of different answers depending on what counts as a city fir whom.

How about Pripyat? Abandoned city near cernobyl, so dividing by population gives NaN.

Population density would give you a good approximation and that list is already compiled.

I think the trick with compiling such a metric is defining it, and it's intended purpose. You've got one: compare the city of commoners to city of wealthy people. Or maybe a rich town locator.

With apartments, you get the sq. ft. of the dwelling, but there's also common areas. None of it being owned by the residents, merely rented. Contrast that with farm land, you'd have relatively few people with high amount of "owned land".

Sometimes very rich people choose to rent in ultra luxury apartments.

I wonder if part of the metric is something like, $ value of land / sq. ft. that is privately owned? Someone in Nebraska maybe owns 50 acres of land that is relatively low demand, versus say... a guy who owns a few golf courses in expensive areas.

kiruna claimed to be the largest city in the world up until 2009 due to the city limits being colocated with the municipality limits as a result of a typo in the paper work. it has a population of 22k and an area of almost 21k km^2^ (~8k sq mi).

You also have to take into account unhoused people. They have the most floor space of all.

My money is on Big Sky, Montana

Perth, WA is the longest city in the world and is only 2.5m people.

Houston, TX immediately came to mind

I would guess cities with declining populations would make it high up in the list.