The standard bankroll is 20 buyins. Say you are playing 1/2. You need 4000 dollars.Of course if you are playing pro you probaly want at least 30 buyins as if you lose your money your're fucked.Edit: Well for every 3 tables i think 20 buyins is good as its quite hard to run bad in all 3 tables. So if you play 12 tables 80 buyins is perfect. Seems like common sense to me, but not 100% sure