Poker is a game of odds. If your odds of winning a hand are shorter than the odds the pot is laying you, you'll want to play the hand. If not, you won't.
For example, if you have to put in $10 to continue with a hand that you'll win 10 percent of the time, the pot will have to be more than $90 to be worth the call. On average you will lose $10 nine times, for a loss of $90, so if the pot when you win on that tenth time is more than $90 (or more than $100 if you include your $10), you will come out ahead.
Pot odds in Hold'em
These odds, more formerly known as pot odds, are usually expressed as a ratio. For example, if it's $10 to you to call and there's $40 in the pot, you are being laid 4-to-1 pot odds. Therefore, if you think your chances of winning the pot are better than 4-to-1, in other words, you will win more than one time out of five, then you should call.
How to use the pot-odds knowledge in the game
How do you know what your odds are of winning? You don't, exactly. Yet, you may have an idea that if you make a certain hand by the turn or river, it will be the winner. If you know your odds to make that hand, you have an easier decision to make. This being the case, there are certain Texas hold'em odds you should know by heart.
If you have four cards to a flush on the flop, your odds of making the flush on the next card are about 4-to-1. This is calculated as follows. You haven't seen 47 cards. As far as you know, there are 13-4=9 of your suit left. This means 38 cards do not make your flush and nine do. So, 38-to-9 reduces to a little greater than 4-to-1. Your odds of making a straight if you have an open-ended straight draw after the flop are closer to 5-to-1. Now there are eight cards (four on either end) that will make your straight out of the 47, or 39-to-8, which reduces to slightly less than 5-to-1. If you're getting better than 5-to-1 pot odds, make the call. With two cards to come you can cut these odds almost in half, but only if you know you are going to see both cards, since if the turn doesn't hit you, you may now be facing another bet and your odds will be 4- or 5-to-1 again.
Other important odds to know
Your odds of flopping a set from a pair are about 8-to-1 against you. Your odds of filling a gutshot straight draw around 11-to-1. The odds that someone at a full table will be dealt an ace are roughly 85-90 percent. If you have an ace, the odds someone else at that full table has one as well is roughly 70-75 percent.
The more situations and related odds you have committed to memory, the faster and better decisions you will make at the poker table. Just memorizing the odds above is sure to make your tough calls and folds a little bit easier.