Total land area of the Earth = 150,000,000 sq km, or 150,000,000,000,000 sq m
Area occupied by a standing man = 0.5 sq m

This means we can pack 300,000,000,000,000 people on Earth, i.e. 300 trillion

edit: this is only a theorycraft. I'm just trying to define the word "overpopulation". Current population is 70 billion, a truly overpopulated earth would be 4000 more populated than what we have now.

Yeah man! If everyone stands we can have 30 trillion people!

But the traffic would be ridiculous.

People are starving now, just because people can fit , does not mean overpopulation isn't a problem.

How much of that can actually be occupied? Look at **** holes like Africa. Nobody wants to live there.

Do you know how much land it takes to nourish a single human?

you made a mistake it's 300trillon.

also you can put more people if there are like 1000floors.

The highest building on Earth has 163 floors (Burj Khalifar), meaning we can multiply the total population by 163 times. i.e. 48900 trillion people, or 48.9 quadrillion people

Okay...how do we feed those?

Let them eat the corpses of the people who starve first?

Well...actually we could have even more - with all land occupied by humans, there's no room for plants. Hence no air to breathe. Hence everyone would be dead. Which means that we could put people on top of each other.