A Straight Flush is five cards of one suit that run in sequence. It is the second strongest hand in the poker hand rankings. Only a Royal Flush beats it, and that hand is itself the highest Straight Flush there is.
How it works
Any five cards of a single suit in order qualify, such as 5♥6♥7♥8♥9♥. Suits are equal in value, so a Straight Flush in spades is not stronger than the same Straight Flush in hearts.
An Ace can play low, which gives A♠2♠3♠4♠5♠ (the steel wheel), or high, which gives 10♠J♠Q♠K♠A♠. The second is a Royal Flush.
There are ten sequences in all, from the wheel to Broadway. The Royal takes one of them, which leaves nine ordinary Straight Flushes per suit.
What beats a straight flush
One hand beats it: a Royal Flush, of which four are possible.
Everything else loses to it: Four of a Kind, a Full House, a Flush and a Straight. Below those: Three of a Kind, Two Pair, One Pair and High Card.
Does a straight flush beat four of a kind?
Yes, and this surprises players who have never held quads. A Four of a Kind is four cards of the same rank, with 624 possible hands. A Straight Flush needs five specific cards of one suit, and there are just 36.
That is a gap of 17 times, and it sets the order: rarer means higher. So even the lowest Straight Flush, A♠2♠3♠4♠5♠, beats four Aces.
Comparing two straight flushes
Compare the top card of the sequence. 9-8-7-6-5 beats 8-7-6-5-4. The steel wheel is the lowest Straight Flush and the Royal Flush is the highest.
Below the Royal there are only nine distinguishable Straight Flushes, ranked by top card from the Five to the King. Each comes in four suits, which is where 36 comes from. Both players need five cards of one suit in order. Two Straight Flushes in one hand mean the board is doing almost all of the work, and the pot is usually split.
Probability
There are two ways to count it, and the numbers are far apart.
- In a five-card deal: 36 combinations out of 2,598,960 - that is 0.00139%, or about 1 in 72,193.
- In seven-card Hold’em: 37,260 out of 133,784,560 - that is 0.0279%, or about 1 in 3,591 hands to the river.
The five-card number comes out in one line: 4 suits x 9 sequences below the Royal = 36. Counting the four Royal Flushes brings the total to 40 hands.
Out of seven cards a Straight Flush lands about 20 times more often than out of five. Most players still see it only a handful of times.