Standard for SNG seems to be 20 buyins. So, when you have $100, that's $5 sng.. $200 for $10, etc..
Um, no.
40 buyins is standard for SNGs and MTTs. If you are really good at SNGs (cashing in more than 50% consistently on 9 person tables --DONs would need to be even higher to break even thanks to rake), you can get away with somewhat less. Larger SNGs should be treated like MTTs.
Consider the cash percentage: a 9 person SNG pays 33% -- pretty good odds if you have a clue. A MTT usually pays 10% -- but the good money, the money that makes it worth much, is at the final table. The odds are much harsher. Some satellites pay a higher than normal percentage, making them more desirable. Some tourneys are very soft, so if you can survive a couple of hard showdowns, you can cash. The
very best online players cash in maybe 15% of the tourneys they play -- but they go much deeper in the ones they cash in than the lesser players. (I'm still trying to figure out how they do that consistently.)
So even the best online tourney players lose 85% of their buyins. Think about that for a sec.
For ring games:
standard is 20 buyins for NL (i.e., if the max buyin is $2, you need $40, for $1/$2 game where the maximum buy-in is $200, you should have a bankroll of at least $4000. )
If the game is swingy, like PLO, double that. If your playing style is looser, double the standard because your variance will be greater. If tight aggressive, the standard is OK.
300 big bets for limit games. Again, adjust for playing style and game.
Note that all these assume you are a good player who wins at a decent consistency. If you are not pretty good, if you are average, BRM will still keep you playing for longer between redeposits.
BRM is to keep you solvent during the downswings, which
will happen. Never assume you cannot lose -- everyone loses at times. The goal in poker is to lose less on your losing
hands, and win more on your winning hands -- which plan has a good chance of keeping you ahead by a slim margin. Grinders play more to maximize that slim margin.
The bottom line is that you choose whether to play patiently and longer at lower limits build up your bankroll by staying within your BRM limits, and going down in limit when you have taken a big hit. Or risking more, going outside BRM limits -- which means risking going broke. Whatever you choose, no whining.
Good luck.