Why Does Deck Size Matter in Blackjack?

You may have listen it many times that fewer decks are leveraged for the blackjack game to get best odds.
If you play blackjack, you’ve probably heard that fewer decks are better for the player. And if all other rules are equal, that’s true. The main reason we say that fewer decks is better for players is that, in each deck, exactly 1/13th of all cards are Aces. 

The house edge is lowest on single-deck games, and increases with each deck added. It’s all in the math. If you start your hand with an Ace, 16 of the other 51 cards, or 31.4 percent, are 10  values that will give you a blackjack. If there are six decks in play, 64 of the other 311 cards, or only 30.9 percent, are 10 values. More blackjacks are dealt with fewer decks, and since players are paid 3-2 on those hands at most tables, that favors players.

Similarly, if the dealer has an 10-value face up in a single-deck game, four of the other 51 cards, or 7.8 percent, are Aces. In a six-deck game, 24 of the remaining 311 cards, or 7.7 percent, are Aces. Again, more blackjacks are dealt with fewer decks, and that’s in the players’ favor.

With fewer decks, you’re more likely to draw a 10 in double down situations. If you have 6-5 in a single-deck game, 16 of the other 50 cards, or 32 percent, are 10 values that will give you 21. In a six-deck game, it’s 96 of 310 cards, or 31 percent. You’ll get that wished-for 10 on your double downs more often with fewer decks.

Why do Double Downs Work Better with Fewer Decks?

If you’re following along closely, you’ve probably already figured out that the same phenomenon that makes blackjacks more likely with fewer decks probably also affects the likelihood of a successful Double Down. If you double your initial hand (6 and 5), you’ll be more likely to draw a face card to form a total of 21 if the game uses fewer decks.

Here’s where things get tricky – don’t forget that your dealer also benefits from these changes at lower deck counts. It’s not just the player that has a shot at more blackjacks. The reason why this fact doesn’t impact the game as much as it might is that players win 3:2 for blackjack, while the house wins just even money. Also, the dealer can’t Double Down, while the player can. That additional doubled-win gives the player a bigger advantage than the dealer.

Increase in House Edge

Earlier, during the 1950s, casinos around the world and in Vegas used one single deck to play a Blackjack game. There were no variations to this game at that time and everybody followed a single game. The house edge was almost negligible. That led changing some of the decks and rules in Blackjack. It includes increasing the deck size to two. This increased the house advantage by almost 0.35%. And now there are Blackjack variants with up to 8 decks that increase the house edge further. At any mobile casino like Jackpot Mobile Casino, you can find the games with a different number of decks. But increase in house edge is compensated by better rules for players. So you need to find your balance.

Counting Cards with Fewer Decks

Counting cards is a popular advantage play technique where a player tracks the relative number of aces and tens in the deck compared to the lower cards. A deck with a proportionally higher number of high cards is more likely to result in a natural and the corresponding 3 to 2 payout.

This means you can raise your bets in certain situations and get a profitable situation. But with more decks in play, it's hard to get into a positive expectation situation. Think about it this way:

You're playing in a single deck game. All the aces have already been dealt. It's not impossible to get dealt a blackjack. It's probably a good idea to flat bet the table minimum at this point. But in a shoe with 8 decks, you still 28 aces left in the deck. Your odds of getting a blackjack have still gone down, but they haven't dropped to 0.

And that works in reverse, too. The low cards are the ones which hurt your chances of getting a natural, so when they get dealt out, the deck improves. The amount that the deck improves is a function of how many decks are in play.

Card counters compensate for these additional decks by converting their count from a running count into a true count. They do that by dividing their count by the number of decks left in the shoe. This isn't the easiest math in the world, which is one reason counters love single deck games so much.

How Many Decks of Cards Are Used In Online Blackjack

In online blackjack, games are generally played with up to eight decks of cards. Additionally, some online casinos may shuffle a single deck automatically at every hand. Virtually, this means you cannot count cards whatsoever in online blackjack.

This computerized reshuffling at each round leads to a randomization of the cards, making it impossible for card counters to implement a solid blackjack strategy. Wondering why online blackjack sites do that? As we know, every deck of cards has a predetermined amount of cards with fixed values. As such, the aces are 1 or 11 and the face cards that are Kings, Queens, and Jacks are 10. These two varieties are the most important cards for a player to get a blackjack.

Now, when at least six decks of cards are so automatically shuffled and randomized, as it happens in online casinos, there are 96 of these high-value cards. Out of these, landing up with a strong 2-card hand that is blackjack or close to 21 becomes difficult. Online blackjack played with multiple decks, as a result, significantly increases the house edge.

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