Dear physics, I'm new to the site. I found it reading this topic: https://www.physicsforums.com/showthread.php?t=145043 I wonder if we could manage to answer, if some not critical precision, the question of: How many people can live confortably, eating only potatos, in earth? As of a first estimation, also used to set an example and the conditions, I'll try to answer. Please, help me correct the estimations, many of them I got from not so trusted sites. 1. How much power we need to function? 2. How much power the earth can give? 3. How much people can live with that? --- 1. From the link above, considering 2000 Kcal per day as a good consumption, we can reach that a human being is like a 100 Watt lamp. (more details on the link) --- 2. Now, to estimate how much the earth can give, we need a lot of assumptions, each one must be checked and corrected if you find it wrong. Thanks. First, lets talk about potatos. I found that a large potato (300g) has approximately 250 cal. It takes 20 weeks to grow from seed. And some estimate that 6m x 6m can produce 200Kg of potatos. That makes ~19 potatos per m^2. That makes 5.7Kg per grow per m^2, or 41g per day per m^2, or still 35 calories per m^2 per day. Now, arable land. This google us to wikipedia, and they estimate 14000 km^2 of arable land, and 50000 km^2 of agricultural land. I'm not sure the difference, though I read the description. But I believe its safe to sum them. So we have 64 thousand km^2 to plant our potatos. That gives us 2600 gigacalories per day. So the earth can produce 127 bilions Watts from potatos. --- Now using 100 Watts per person, every one eating his 8 potatos per day at lunch and dinner, the maximum confortable population would be only 1 billion 300 millions. And here, looking this number, I think there should be serious problems with this estimation! Please, any lights to share? Thanks, Beco.