What do you mean "retire"? Can't you do that for free anytime you want?
he mean no more work, just an happy life
i would say 1M dollar at least
You can do that already for almost nothing if you have a couple friends. Just chill, you don't need 1M dollar to do nothing. But why would you want to do nothing anyway?
Oh I know, maybe by "work" you mean something that somebody else wants you to do but you don't really want to do so much yourself apart for some financial gain?
You need money to do "nothing". If you want to live a stress free life you need at least 1M. Other than that will require a constant source of income that is most likely not going to be passive, so you aren't doing nothing. (doing nothing = having free time).