The rule of four-two, is an easy way to figure the odds for any situation where you know your outs. It is not completely accurate but it will give you a quick "ballpark" figure of your chances for making a hand. Here is how it works.
With two cards to come after the flop you multiply your number of outs by four. With one card to come after the turn, you multiply your number of outs by two. This will give you a quick figure to work with. If you have a four-card flush after the flop you have nine outs. With two cards to come, you multiply the nine by four and you get 36 percent chance of making the flush. The true odds are 35 percent. With one card to come you multiply nine by two and get 18 percent. The true figure is 19.6. It is not completely accurate but it is pretty close.