How Many Decks in Blackjack, and Does It Matter? We Played 200 Million Rounds to Find Out

The short answer

Blackjack is usually dealt from 6 or 8 decks in casinos, with some 1- and 2-deck games still around. Fewer decks are better for you, but the difference is smaller than most people think: going from eight decks to one is worth about four-tenths of a percent. A single bad rule, like a 6 to 5 payout on blackjack, costs you far more than that.

Our results: 40 million rounds per deck count

We used the same rules for every run: dealer stands on soft 17, peeks for blackjack, double on any two cards and after splits, split to four hands, late surrender, blackjack pays 3 to 2, and a cut card 75% of the way through the shoe. The player used perfect multi-deck basic strategy and never took insurance.

Each house edge figure is accurate to about ±0.02%. The blackjack chances are exact for a fresh shoe.

Three things stand out:

• Single deck with good rules is roughly a break-even game for a perfect basic strategy player. Our single-deck run actually used the multi-deck chart, so a chart built for one deck would do very slightly better still.
• The biggest jumps come at the low end. One deck to two costs about 0.22%. Two to four, about 0.13%.
• Six versus eight barely matters. The two are within a hundredth of a percent of each other.

Our numbers line up with the standard published rule effects. The Wizard of Odds lists one deck as worth +0.48% to the player relative to eight decks, two decks +0.19%, four +0.07% and six +0.02%. The small gap at the single-deck end is the chart difference mentioned above.

Why fewer decks are better for you

It comes down to card removal. In a single deck, every card that's dealt changes what's left by a noticeable amount. In an eight-deck shoe, one card barely moves anything.

Most of those shifts happen to help the player at the moments that matter:

• Blackjacks come a little more often. Once you have an ace, there are relatively more tens left for your second card in a small deck. That's why the chance of a natural rises from 4.75% with six decks to 4.83% with one, and each of those pays 3 to 2.
• Doubles get stronger. When you hold a small-card 10 or 11, those small cards are gone from a single deck, so the cards left are a bit richer in tens. Your one card after doubling is more likely to be a good one.
• Pairs and stiff hands shift too. When you split or stand, the cards in your hand aren't available to the dealer, and in a small deck that matters.

None of this means you can feel it from hand to hand. It shows up over tens of thousands of hands. Luck still runs the short term; see is blackjack luck or skill? for how long the edge takes to show.

Why casinos use six or eight decks

If fewer decks help the player, why are most tables dealt from a six- or eight-deck shoe? A few reasons:

• It's cheaper for the house. Even a few tenths of a percent adds up over every hand at every table.
• Less shuffling, more hands. A big shoe deals many more rounds between shuffles, and shuffling time is time the table isn't earning.
• It blunts card counting. Counting works because card removal matters, and in a big shoe each card matters less. Casinos also reduce counting with shallow penetration (shuffling earlier) and continuous shuffling machines, which return cards to the shoe after every round. Our guide to card counting online covers how counting works.

The single-deck catch: 6 to 5

Here's where single deck stops being a bargain. Many single-deck games, especially low-minimum tables on the Las Vegas Strip, pay 6 to 5 on blackjack instead of 3 to 2. The Las Vegas Advisor describes 6 to 5 as the standard at most such tables.

That one change costs you about 1.4% (the Wizard of Odds puts it at 1.39%). Compare it with our table: the whole benefit of one deck over eight is about 0.4%. A 6 to 5 single-deck game is worse for you than an ordinary 3 to 2 game dealt from eight decks, by roughly a full percent.

The same goes for the dealer's soft 17 rule. A dealer who hits soft 17 adds about 0.2%, which is as much as going from two decks to six. Our guide to blackjack dealer rules explains why.

Does deck count change basic strategy?

A little. The core of the chart (hit and stand decisions against the dealer's upcard) is the same for any number of decks. The differences are at the margins: a few doubles and splits that are slightly better with one or two decks. For example, single-deck charts double more often with small totals like 8 and with some soft hands.

If you're learning, use one chart and stick to it. The multi-deck chart in our basic strategy guide is built for BlackJack Streak's default six decks, and as our single-deck run shows, it still plays one deck almost perfectly.

Choosing the deck count at BlackJack Streak

At BlackJack Streak, the shoe defaults to six decks, the casino standard. Open Settings and you can pick 1, 2, 4, 6 or 8 decks. The setting's hint puts it in one line: "More decks is the casino standard; one deck is slightly better for you."

• Changing decks starts a fresh shoe. Rule changes take effect from the next hand, and the new shoe is sealed with its own fingerprint before it's dealt, like every shoe at BlackJack Streak. See how the provably fair shuffle works.
• The cut card sits at 75% of the shoe, whatever the size. With one deck that means a reshuffle after 39 cards.
• At a table with friends, the host picks the deck count for everyone.
• Want no deck effects at all? Settings can also shuffle a brand-new shoe before every hand.

Because the chips are free, it's a good place to feel the difference yourself: play a few hundred hands at one deck and a few hundred at eight, and compare your stats. Just don't expect the gap to show up quickly. At 0.4%, it takes a lot of hands.

Sources

• Blackjack rule variations, Wizard of Odds (effect of 1, 2, 4, 6 and 8 decks; 6 to 5 payout; dealer hits soft 17)
• What's so bad about 6-5 blackjack?, Las Vegas Advisor
• Card counting, Wikipedia (penetration and continuous shuffling machines as countermeasures)
• House edge by deck count: our own simulations, 40 million rounds per deck count through BlackJack Streak's rules engine