Human population over the globe is increasing rapidly and it seems that growth will continue in future too. The question arises that how much it can grow and what size of population our earth can hold conveniently? Research based convincing answer is expected from experts and researchers.
UN's FAO gives a lot of information on world food supply and its perspectives: http://www.fao.org/worldfoodsituation/en/ . The Wikipedia entry (https://en.wikipedia.org/wiki/Human_overpopulation#Global_perspective_on_food_supply) discusses this shortly, but refers only to newspaper articles, not to scientific literature. But there is a large number of books on overpopulation, starting from Thomas Robert Malthus to modern ones (see https://www.google.com/search?q=population+earth+can+support&tbm=bks and similar searches with Google's Books Search). However, I agree that more research is needed, as well as political answers.
Thanks Wolfgang R. Dick for your kind concern and for providing valuable information.
I think the essence of your question is the meaning of 'conveniently'. Over-consumption of goods, wasteful practices, lack of efficiency and ineffective recycling of materials all contribute to a larger ecological footprint than needed in many countries.
Largely, it is then a matter of energy and material consumption, both of which can become more effective. Energy consumption can become more effective by smarter practices but also less important with the improvements in nuclear fusion and renewable energy solutions such as improved efficiency and storage of solar power. Material consumption can also become more effective by smarter practices and also less important with improved recycling practices and the mining of asteroids and extraterrestrial colonization that can provide rare materials needed in many production lines.