Isn't that a lot to risk? How big should my bankroll be in terms of tourney buy-ins?

I've heard that for limit cash you should have 300-500 BB in your bankroll, so like if you're playing 2/4 you should have $1200-$2000 in your bankroll...is that the same for SNG's? shouldn't i have like 50-60 buy-in's? or I am being too conservative on this issue?