Determining the bankroll needed for a 4-hour blackjack session involves considering factors like your betting strategy, average bet size, and the pace of play. A common guideline is to have a bankroll that is 50 to 100 times your average bet to withstand fluctuations and avoid going broke during the session. Additionally, if you plan to play higher stakes or use aggressive betting strategies, you may want to aim for the higher end of that range. It's essential to assess your personal risk tolerance and playing style when deciding the appropriate bankroll.