The ability to calculate pot odds is a necessary part of any poker players game. Our goal is to play the law of averages as opposed to blind luck, in determining whether or not calling a bet is a profitable decision.
Pot odds decisions are one of poker's most elementary, yet it is one of the most common mistakes made by amateur players at all levels. No matter if you are playing a nickel/dime no limit game at Absolute Poker or the $100/$200 table at Party Poker, you will always find a player who is making bad pot odd decisions or ignoring them entirely, meanwhile paying off the rest of the table!
The most straightforward explanation of how to calculate pot odds is to compare the total number of unknown cards to how many outs you have, and then do some simple division.
For example, if you are four to a nut flush on the turn of a Texas Hold 'em game, there are 46 unknown cards, (52 minus your 2 pocket cards and 4 on the board). Of those 46 cards, 9 are the same suit as your flush draw. So 37 cards will not help you, while 9 will give you the nut flush hand.
Your odds are : 37/9, or more simply, 4.1 to 1 odds against making your draw.
A good poker player will only call a bet in this case, if there is already 4x that amount already in the pot. So if you were playing a game of $5/$10 limit, then there would need to be at least $40 already in the pot to justify your calling that $10 bet to see the river.
How about those inside straight draws that are so tempting to hang onto? You have 4 outs, with 46 unknown cards on the turn. 42 cards are no help, 4 make you the winner. 42/4 = 10.5! You would need over 10 times the amount of your call to be in the pot already, to justify this decision. Only in a wild game of poker will this kind of call pay off in the long run.