How much land does one need to become self sufficient? Let's assume that means producing enough biomass to generate the resources necessary to have a surplus of food or money.
I worked really hard on our family "farm" all my childhood and that's maybe the only thing that helped us survive. Although we did experience hunger from time to time.
It's not even a question of land, it's a question of how much work you can put into that land. It's a backbreaking work every day.
It's a good option if society collapses and there's no other option to survive. Otherwise, it's just not worth it. Millions of current Russia population hate working on the land because they already have that inoculation from 90s.
Our agriculture (Ger) is completely dependent on workers from abroad. If you send the average office worker on a field, he will probably collapse after a day or two.
Friends of mine have some chickens and that alone causes so much work everyday... They give away the eggs which is nice for us. Selling them wouldn't even pay for the fuel to transport them anywhere. Same with most other kinds of produce.
"Self sufficient" where you buy things from the supermarket is just greenwashing cosplay. Just like a "self driving" car where you can't take your hands off the steering wheel.
Of course you could scrap the electricity and get your water from the nearest river, but I doubt many people would want to put up with that.
Most people wouldn't want true self sufficiency if they could have it. I admire people who "go into the woods" for years (they are generally more hunter/gathers than farmers); but even as introverted as I am, I still like to have a larger group of people around me.
Where do you get the iron for your implements? Or are you going to use wooden hoes?
Where do you get medicine, when you need it?
Where do you get clothes?
Et cetera.
For clothing, you grow it. Between Flax, wool, furs, and cotton you can grow something anywhere (except near the poles). Having to grow clothing and shelter more than doubles your needed land area in some places.
Sill it requires a lot of work. And I doubt that it is possible to be 100% self-sufficient.
There're many things farmer needs that are produced by other people. From tools like shovels to water pumps to animal fodder (which is also very expensive).
It's a nice thing to try though, to prepare oneself for some nasty events. When COVID-19 started I was thinking that if the world comes to an end, at least I'll be able to survive somewhat longer than others with my skills. I know how to grow my food. Didn't do it for a long time, but it's hard to forget the basics.
It's nowhere near self sufficiency though. The amount and the variety of things you eat today is tremendous and coming from many places, you're not going to cultivate a fraction of that at home.
If you're talking bare subsistence, 1-2 acres of wheat should be enough to feed a family in grain/bread.
3-4 acres should be more than enough for the basics for a _small_ family, if you accept to buy the more exotic items from a store, and that you will probably never grow fat.
It does require quite a bit of machinery though- several tractors plus all the attachments (plowing, harvesting, cutting etc).
Maybe the permaculture people, or intentional communities that seek to be self-sufficient (as a community); perhaps kibbutzim hold useful knowledge here?
The typical term is 'homesteading' and there are tons of resources for it. My aunt does it and is part of a collective and it's nearly a full time job.
(There are many opinions so I don’t put one particular source here.)