I listen to a podcast about eCommerce and most of the people interviewed have their own business, many of which have revenues in the millions. The host asks a set of common questions to everyone including what their number would be where the would feel like they never had to work again (FIRE basically). Almost all of them say $5 million or more.
Personally at $1,000,000 or so even with a family of 7 I think we'd be fine. After all, I could always earn some extra money on the side to supplement that. To be totally FIREd and never work another day in my life it would probably be a bit higher, maybe $1.3-$1.5 million. I haven't spent too much time trying to nail it down exactly as it's going to be a long ways off with a single income and lots of mouths to feed (and house, and clothe, and educate, etc.)