There is a facebook post that says the entire population of the planet could live in 2000 square foot houses just in the state of Alaska.
Some research shows that there are roughly 1585682383 households on the planet. Alaska is 663,300 mi².
I dont think Im doing the math correctly..... households x 2000^2 Then converting that number to miles^2
On
So the total area of all the houses would be $$ 2000\text{ sq.ft.}\times 1\,585\,682\,383 = 3\,171\,364\,766\,000\text{ sq.ft.} \approx 3.171\cdot 10^{12}\text{ sq.ft.} $$ Now, a square mile is roughly $2.788\cdot 10^7 \text{ sq.ft}$. How many square miles do all those hoseholds take up? We get $$ \frac{3.171\cdot 10^{12}\text{ sq.ft.}}{2.788\cdot 10^7 \text{ sq.ft}/\text{sq.mi.}} = 1.137\cdot 10^5\text{ sq.mi.} $$ which, compared to Alaska's total area of $6.633\cdot 10^5 \text{ sq.mi.}$ means that we only use a sixth of the total area. Each of the one and a half bilion houses can come with roughly $10\,000$ square feet of back gardens before you fill up the entirety of Alaska. Alternatively, you could fill Alaska with such houses wall-to-wall, and there would be roughly a house to each person in the world, if all the houses are only ground floors. Start building the $2000$ square foot houses with several floors, and you save enough ground space to make streets.
$1$ mile is $5280$ feet. So 1 square mile is $5280^2 = 27,878,400$ square feet. If one house is $2000$ square feet, the you can have $27878400 / 2000 = 13939.2$ houses per square mile. So in $ 663,300$ square miles you can have $ 663,300 \cdot 13939.2 = 9,245,871,360$ houses.
This, of course assumes that you have no space between houses and that the terrain allows for houses all over.