While a Malthusian catastrophe may yet be avoidable, with more than 7 billion people on the planet, space is in decreasingly short supply. Still, I wonder, how much more crowded could it get. Not practically or realistically, but hypothetically. Forget about pesky matters like having to farm for food. How many people could fit on Earth if every square mile of land was used no matter how inhospitable the climate or topography. Mountains, swamps, deserts — all of it. To make it less abstract and to use conditions that people actually live in, let’s use the population density of the world’s most crowded megacity: Dhaka, Bangladesh.
Different sources vary but Demographia estimates Dhaka’s population at 16,235,000 with a density of 44,110 presumably irritated people per square kilometer (114,300 per sq. mile). By comparison, NYC is only one quarter as crowded. What makes Dhaka’s density even more remarkable is that it’s a low-slung city with few towers to spread people up into the vertical.
Filling the World
According to the CIA’s World Factbook, the Earth's surface area measures 510,072,000 sq. km. (196,940,000 sq. miles). 70.8% is water with 148,940,000 sq. km. (57,510,000 sq. miles) of land taking up the remaining 29.2%. So all we need do is multiply this area by the Dhaka density of 44,110 per square kilometer to get to...6,569,743,400,000?
Let's write that out.
6 trillion 569 billion 743 million 400 thousand
My brain refuses to accept it even though it’s grade school math simple. It's more than 850x the current world population.
The other extreme
Perhaps you're wondering about the opposite end of the spectrum. That would be Mongolia with a population density of an almost non-existent 2 people per square kilometer. This is of course an entire country instead of a city, but it makes a perfect contrast for the way people live.
If we peopled the world at the Mongolian rate we'd get just bit less than 298 million in total. 148,940,000 sq. km. of land x 2 per square kilometer = 297,880,000 million. Or just 1/24th the current world population.