POT ODDS
OUTS ON THE FLOP FOR THE TURN ON THE TURN FOR THE RIVER ON THE FLOP FOR THE TURN AND RIVER
1 2.2% 2.2% 4.3%
2 4.3% 4.4% 8.4%
3 6.4% 6.5% 12.5%
4 8.5% 8.7% 16.5%
5 10.6% 10.9% 20.4%
6 12.8% 13.0% 24.1%
7 14.9% 15.2% 27.7%
8 17.0% 17.4% 31.5%
9 19.2% 19.6% 35.0%
10 21.3% 21.7% 38.4%
11 23.4% 24.0% 41.7%
12 26.0% 26.1% 45.0%
13 28.0% 28.1% 48.1%
14 29.8% 30.4% 51.2%
15 32.0% 32.6% 54.1%
16 34.0% 35.0% 57.0%
17 36.2% 37.0% 60.0%
18 38.3% 39.1% 62.4%
The above referenced chart will help you determine the odds against improving your hand on the turn and/or the river.  When playing online you can either post this chart next to your computer or use some of the Odds Calculators that are available.  However, when playing in a live game you must memorize these odds.  Another way to determine your odds, is to multiply your outs times 4 (if the turn and river are yet to come) or times 2 (if there is only 1 card left to come).

Remember, that this Odds Chart can also be useful to determine the size of the bet you want to make.  For example, if you put your opponent on a hand that suggests that he needs only 1 card to make his hand with two cards to be seen, then you must bet more than 4.3% to make calling you or raising you incorrect.