Texas Hold'em is played for a wide variety of limits. What all of these limits have in common is that they adhere to the same betting structure, which is a 1-2 ratio. The bets before the flop and on the flop will be exactly one small bet, the lower betting tier, and the bets on the turn and river will be exactly one big bet, the higher betting tier (twice the small bet).

The most common betting limits are $1-$2, $4-$6, $4-$8, $5-$10, $10-$20, $15-$30, $20-$40, $30-$60, $60-$120, $100-$200 and $300-$600. You must bet exactly the amount mentioned and that is why this is called structured game. You are not free to bet, for example, $4 or $5 in a $3-$6 game.

Another betting structure that has become very popular is called $1-$4-$8-$8 Limit. This means that you may bet from $1 to $4 before the flop, and you may bet from $1-$4 after the flop. On the turn you can bet between $1 and $8 and you can make the same bet on the river.