Count the number cards that can complete your straight. This is the number of possibilities for completing the straight. If you have an open-ended straight, your odds are twice as high as with a closed straight. For example, if you have 9-10-J-Q, either an 8 or a K could complete your straight, so it is open-ended. You have eight ways to complete the straight because you could draw any of the four eights or kings. However, if you have 9-10-Q-K, you would only have four ways to complete the straight because you could only draw one of the four jacks.
Count the number of cards you could draw, which are the number of possible outcomes. For example, if you have five cards in your hand, there are 47 cards remaining in the deck.
Divide the number of cards that could complete your straight by the number of cards remaining in the deck to find the probability of getting your straight in poker. If you have an open-ended straight, with eight possible cards, divide 8 by 47 to get a probability of 0.17, or 17 percent. If you have a closed straight, divide 4 by 47 to find the probability equals 0.085, or about 8.5 percent.