Pot Odds!!! Keeping track of the pot...

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Like every other poster said, just count number of small bets preflop and flop as the action orbits around the table. Then on turn & river convert small bets to large bets.

A trick my brother uses when drunk, is to just look at the rake schedule. For example, in a 10/20 game the rake is two on the flop, 1 at 80 and 1 at 160. So he looks at the rake and says (for example), 'oh tghe rake is 3 so the pot is at least 80.'

This second method is not as good as the first, but it gives a rough idea if you lose count or forget to count. However, some dealers don't rake the pot at the exact time it crosses the threshold values.

Another quick trick is to, for passive games, just look at the number of players in the pot & consider it against what draw you are trying to complete. For a limit game that is loose-passive, it is almost always correct to draw to the flush with a 4-flush or the up-n-down straight draw with at least 4 players in the pot. However, that same draw would have negative expectation when heads-up in a small pot.