I got frustrated with Elons claim that the surface needed to power the entire world by solar *only takes a few hundred miles squared of solar cells.

There's no such thing as *only a few hundred miles by a few hundred miles. The circumference of the earth is just 40,000 km so that's probably a gigantic footprint, right?
Well, the circumference isn't the surface area, so I start googling, I casually like math, so how do you derive the surface area of a sphere from its circumference?
Google gives me just 3 sources in the top two pages that even attempt to answer my question:

> https://math.stackexchange.com/questions/1866812/deriving-surface-area-of-a-sphere-from-the-circumference

> https://sciencing.com/how-to-calculate-the-surface-area-of-a-circle-12751758.html

> http://mathcentral.uregina.ca/QQ/database/QQ.09.06/s/amanda4.html

Turns out every single one of these is inconsistent with the others, and also demonstrably incorrect, the answer is obvious once you check the circumference and the surface area of the earth.
Anyway; once you have the surface, you can check how big of a portion a few hundred square miles is. But what if you just compare it to habitable land area? Or better yet, area that's already inhabited?

I can't trust google now, so what is the area of inhabited land in the world, /sci/?

The correct formula, in case you were wondering is:
$A = \frac{C^2}{\pi}$