After the flop, it is the number of unseen cards that can improve a hand
(outs), which determine the probability of improvement on the turn or river. For
example, if you have an open-ended straight-draw, eight cards are out that will
improve your hand to a straight (four of each rank on each end). With two cards
to come, you have a 31.5% chance of making the straight, but with one card to
come, the chance drops to 17.4%. Next is a tabulation of common draws and the
chances of improvement. Knowing these probabilities is essential for computing
the pot odds when betting on the turn and river cards. For situations not listed
in the table, count the number of outs to make the hand and read the percentage
next to the number of outs.
Probabilities for Improving a Hand
A more useful way to think about drawing hands is to examine the minimum amount of winnings needed to justify the cost of continued play. The tables that follow show for the number of available outs, the minimum pot size that must be won to justify the cost. If you cannot win the minimum amount shown in the table under the cost column, your bet is not getting the correct pot odds
There are two tables, one for two cards to come and the other when there is one card to come. For example, playing $3-6 Hold'em, you are on a flush-draw (9 outs) with two cards to come. There is a $6 bet to call and you expect to spend $12 total to get to the river. In the table for two cards to come, the intersection of the $12 column and 9-out row shows $34. You must win at least $34 to justify spending $12, because in this situation, you will have about two failures for every success.
For higher betting limits, multiply the dollar amounts by 10. Example: In a $5-10 game, you are on an inside-straight-draw (4 outs) and must call a raise ($20) to see the last card. In the table for one card to come, think of the $2 column as the column 1 for $20. The value in the row for 4 outs is multiplied by 10 to 2 give $230. You must win at least $230 to justify a $20 bet on 2 an inside-straight-draw. These tables are especially useful for 4 Internet competition, because pot sizes are precisely displayed on 5 your screen and the table can be in front of you for reference.