What you think is Earth's maximum occupancy?

I have read that if the entire Sahara desert and the continent of Australia were intensively irrigated and farmed, our Earth could support 100Billion people or more. Actually, over 2/3rds of all the people on Earth live in a relatively narrow band of land within some 400 miles from the seacoast from Iran to Japan. This is less than 10% of the total land area. The rest of us (less than 1/3 of everyone) live on the remaining 90% of the land. Actually, over 40% of the land is almost devoid of any significant human presence.

I personally would not want to share the Earth with 100Billion other humans, but thankfully, such a scenario is highly unlikely. The World Health Organization predicts that the world population will peak at ~9Billion at around the year 2100, and then begin a slow decline. I believe in 500 years or so, nearly all humans will be required to leave Earth, to allow it to return to its former wild state. I can't wait.

as far as food goes, we already produce enough to feed over 12 billion people, yet due to distributioin problems and livestock agriculture almost 1 billion people face starvation. The biggest problem is not related to a number. Even if population stabilised and remained at 7 billion if that same number of people started using more energy, land and resources then we'll face a disaster. The issue that's most likely to hurt the most is water shortages or water becoming incredibly expensive like desalination is.

10-12 billion. 20 billion if you're committed to burning the Earth. That said, with the way resources are currently being used, asking the system to support more than 5 billion isn't a good idea. Population is expanding faster than our infrastructure is growing.

In terms of degradation of the environment and global warming in exchange of material goods vs. uncontrollable weather and sea elevations endangering low land flooding ....we have passed a rational population maximum a long way back down the road.

There is a lot of empty space to fill on this planet.