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Number of cattle: 1.5 billion in the world.
Weight, I dunno. A newborn calf can be 25-45 kg, as much as a small woman on the upper end. 700 kg for an adult cow or steer, 1100 for an adult bull. I don't know how many are meat vs. working animals, and presumably meat animals don't stay as adults for long. Let me guess an average mass of 300 kg.
Say an average human is 75 kg. That means the biomass of cows today could instead be another 6 billion humans, for a total of 13 billion. They wouldn't even have to be strict vegetarian humans, just need everyone to replace beef with vegetables; chicken and pigs and such would still be around.
Of course, that replacement might not be trivial, if most of the cattle are eating grass; you'd have to turn pasture into farmland. But still.
(ETA: USA has 90 million cattle, suggesting we could feed another 360 million Americans.)
***
So, potatoes are crazy. The Dutch produce 44.7 tonnes per hectare. You can feed someone for a year with about a ton of potatoes, or less, so that's nearly 4500 people per square kilometer of potato farm. Maybe 5000. The Dutch are top, but other northwestern European countries also produce similar amounts. Italy and Spain are down at 25-28 t/ha, eastern Europe around 13, for only 1300-1500 people per km2. I don't know why the differences. Climate, water, fertilizer?
There's about 14 million km2 of arable land (out of 48 million km2 of agricultural land), so if that all was growing potatoes at similar rates, that could support from 18 to 70 billion people, vs. the 7.1 billion of today.
Why so much? According to Charles Mann, potatoes produce 4x the edible dry biomass that wheat does. Why that, I don't know; I'd guess being able to put most mass into the tuber, rather than stalk. Of course stalks can be fed to livestock or furnaces or industry, so wheat chaff can turn into useful things. But for straight food production I'm guessing root crops rule.
Another source gives 189519 hectograms per hectare for the world in 2012, or about 19 tons per hectare, vs. 4.5 tons/ha for rice. Maize is 4.8, other cereals less than rice, with wheat at 3; taro is 7.6, cassava 13. Those numbers aren't so far apart in calories: potatoes are 22% dry biomass, wheat 88% (Mann again.) The gap's narrowed since the 1760s, when Andrew Young found eastern England producing 1500 lbs/acre of wheat, but 25,000 lbs/acre of potato, for 4x the calories per acre. (That, or England's just better at producing potato.) If maize is like wheat, it's slightly more food per land than potatoes. (Though I think potatoes are a more complete food.) Of course, most US corn is fed to livestock, bringing us full circle.
Potato land is given at 193,000 km2. Maize, rice, and wheat add up to about 5.5 million km2, leaving a lot of arable land growing other stuff. Soybeans are another million.
Arable land is 9% of land. Scaling somehow up to 33% of land, and using the highest number, that'd support 250 billion people. Trillion person Earth would need 4x the highest national level potato yield. Challenging.
***
So, between a vegetarian diet and more optimal growing conditions, there seems to be room for a bunch more humans. Possibly a lot more humans.
Weight, I dunno. A newborn calf can be 25-45 kg, as much as a small woman on the upper end. 700 kg for an adult cow or steer, 1100 for an adult bull. I don't know how many are meat vs. working animals, and presumably meat animals don't stay as adults for long. Let me guess an average mass of 300 kg.
Say an average human is 75 kg. That means the biomass of cows today could instead be another 6 billion humans, for a total of 13 billion. They wouldn't even have to be strict vegetarian humans, just need everyone to replace beef with vegetables; chicken and pigs and such would still be around.
Of course, that replacement might not be trivial, if most of the cattle are eating grass; you'd have to turn pasture into farmland. But still.
(ETA: USA has 90 million cattle, suggesting we could feed another 360 million Americans.)
***
So, potatoes are crazy. The Dutch produce 44.7 tonnes per hectare. You can feed someone for a year with about a ton of potatoes, or less, so that's nearly 4500 people per square kilometer of potato farm. Maybe 5000. The Dutch are top, but other northwestern European countries also produce similar amounts. Italy and Spain are down at 25-28 t/ha, eastern Europe around 13, for only 1300-1500 people per km2. I don't know why the differences. Climate, water, fertilizer?
There's about 14 million km2 of arable land (out of 48 million km2 of agricultural land), so if that all was growing potatoes at similar rates, that could support from 18 to 70 billion people, vs. the 7.1 billion of today.
Why so much? According to Charles Mann, potatoes produce 4x the edible dry biomass that wheat does. Why that, I don't know; I'd guess being able to put most mass into the tuber, rather than stalk. Of course stalks can be fed to livestock or furnaces or industry, so wheat chaff can turn into useful things. But for straight food production I'm guessing root crops rule.
Another source gives 189519 hectograms per hectare for the world in 2012, or about 19 tons per hectare, vs. 4.5 tons/ha for rice. Maize is 4.8, other cereals less than rice, with wheat at 3; taro is 7.6, cassava 13. Those numbers aren't so far apart in calories: potatoes are 22% dry biomass, wheat 88% (Mann again.) The gap's narrowed since the 1760s, when Andrew Young found eastern England producing 1500 lbs/acre of wheat, but 25,000 lbs/acre of potato, for 4x the calories per acre. (That, or England's just better at producing potato.) If maize is like wheat, it's slightly more food per land than potatoes. (Though I think potatoes are a more complete food.) Of course, most US corn is fed to livestock, bringing us full circle.
Potato land is given at 193,000 km2. Maize, rice, and wheat add up to about 5.5 million km2, leaving a lot of arable land growing other stuff. Soybeans are another million.
Arable land is 9% of land. Scaling somehow up to 33% of land, and using the highest number, that'd support 250 billion people. Trillion person Earth would need 4x the highest national level potato yield. Challenging.
***
So, between a vegetarian diet and more optimal growing conditions, there seems to be room for a bunch more humans. Possibly a lot more humans.