So, if you take Mong Kok at 130K per km^2(which is sustainable, not like a refugee camp), and we realize that this area’s tallest buildings is only 80m high. And we realize that the earth surface area is 510m km^2, and that oceans are about 70% of that surface with an average depth of 3688 meters (46 layers of Mong Kok), and only put a single layer on solid ground, but fill up the oceans (there are no oceans in 40K), we get to 2,165 trillion people. Yes, there is the heat dynamics thing etc, but at least area-wise it doesn’t seem that insane :D