The core difference: chips vs money
In a cash game, chips represent real money at a fixed rate. You can sit down or leave at any point, and your stack reflects your current profit or loss. In a tournament, chips have no cash value — your entry fee buys chips to play with, and the payout depends on finishing position.
Variance and session length
Cash games allow shorter sessions and more consistent results over a smaller sample. Tournaments compress variance: a single deep run can represent weeks of cash-game volume in terms of profit, but most entries do not reach the money.
Bankroll requirements differ
A standard bankroll guideline for cash games is 20-30 buy-ins for your stake. For tournaments, 50-100 buy-ins is common because the variance is higher and deeper runs are rare. The right format depends partly on the bankroll you have available.