According to [1], 2 billion people are subsistence farmers with under 5 hectares. The population adjusted average seems to be around a quarter of a hectare (~0.6 acres) per person (which sounds low to me, as someone who has grown my own food without automation).

10^9 == many of us. Unless your definition of "us" is hacker news readers.

[1] https://en.wikipedia.org/wiki/Subsistence_agriculture