This question already has an answer here:
As the world continues to increase in population, what is considered to be the limit in terms of amount of habitable living space and resources?
A couple of assumptions:
Famines are not (or very rarely) caused by wars, terrorism, dictatorships, corrupt governments, corporate exploitation, etc.
Resources can be distributed quite easily.
Problems using land for living space and resources that arise from simply not having the technology, or political/economic will have been overcome.
What I'm trying to figure out is what the limit is before actually moving some of the population to another planet becomes a desirable alternative, but assuming that by the time we have the technology to do that, we also have the technology to resolve our resource issues.