back when BioSphere 2 was the rage it was easy to calculate what that model would look like spread over the whole planet. IIRC if 8 people lived in an area the size of biosphere 2 then 60 Billion could live on the planet Earth. Granted there were flaws in the biosphere 2 experiment such that the folks actually lost weight and couldn't build open fires due to slow rate of oxygen replenishment, couldn't use pesticides because the food cycles were too short, but still as an "upper limit" (somewhat beyond actually) it's a useful benchmark.
If you don't recall, Biosphere 2 had an "ocean" and a "desert" which for my calculations above I assumed were in roughly equal proportions to what's on Earth.
But that said, doesn't mean we're not about to encounter some extremely unusual times for our planet and species. What happens to the housing industry when population is stable? How much spare capacity is there in our food supplies if say a current major source is hit with a calamity (drought, fire, flood, etc)?