So I know we can and should defer to expert opinion, but I like giving things a stab myself first. So let’s run through this. We have six acres per person. What will we do with it?
I’m going to look at this from a temperate moderately wet perspective. This will be lower then needed in the far North or the Desert, higher then needed in the tropics. So it should balance out.
First and most obvious, the built environment. Let’s be generous and give everyone an acre for a house, sheds, outbuildings, their share of the roads and parking lots (1/10 of an acre per person in the USA, though much of that could be depaved) and public buildings.
Then food raising. An acre per person should be plenty. An intensive garden of vegetables and potatoes, and a food forest/ orchard which is more extensive but resilient. It also provides beauty and habitat.
Fuel; there are widely different opinions online as to how many cords of wood can be sustainably take from an acre of forest. A
rocket stove can heat a building with 2 cords of wood a year. More then one person should inhabit a building. So let’s talk a low estimate of half a cord a year per acre, and give each person an acre of woodland. This also provides habitat and protects watersheds.
Mining should be unnecessary with all metals recycled.
Recreation should be a snap with half the earth in protected status, and a garden full of plants.
Other; clothing, crafts, furniture, charcoal for cottage industries, feedstocks, paints, lime etc. Most of this could come from managed woodland; so we will give each person another 2 acres.
Now we are left with an acre over per person. This could cover shortfalls, be used for even more habitat, or raise animals if we don’t go vegan. Even if we did, we would probably raise some animals for transport; so the remaining acres 8 million acres, pooled together, could partially be used to raise some livestock. (Though some livestock could probably forage in the forests.)
So there we have a world which is half protected wilderness, and the remaining half largely trees, inhabited by 8 billion happy people; it wouldn’t be the American dream, but who wants that anyhow!