How do you calculate the probability of a royal flush?

Answer 1

First, we determine the total number of five card hands possible. Since there are 52 cards, we simply pick the first card 52 ways, then the second card 51 ways, then the third card 50 ways, then the fourth card 49 ways, and finally the fifth card 48 ways. This gives a total of 52*51*50*49*48. Since the order that we pick the cards is unimportant, we divide this total by the number of ways of permuting five objects, which is 5! = 120. So, the total becomes 52*51*50*49*48/120 = 2598960. Note this is just (52 choose 5).

Now that we know the number of possible hands, we simply divide the number of royal flushes (4) by the above 2598960:

4/2598960 = 0.000001539, the probability of getting a royal flush in the first 5 cards off the deck.

Of course, depending on the type of Poker being played, the probability will differ from this value. Omaha has a higher probability than Texas Hold'em, which has a higher probability than calculated above. Wild cards can drastically change the probability. If every card in the deck is wild, then the probability is 1 (if 5 of a kind isn't allowed) or 0 (if 5 of a kind is allowed).