# In Blackjack, why does the number of cards in a deck matter?

You’ve probably heard this a million times, but your odds of winning at blackjack improve if fewer decks are utilized.

## Do you ever pause to consider the reasons for this?

This piece was inspired by a question I was asked by a friend who isn’t a big gambler. He has begun his preparations for a bachelor party in Las Vegas by learning the game of blackjack. He had picked up on the common belief that “fewer decks is better,” but he was still confused. After all, he reasoned, regardless of how many decks are combined, the overall proportion of each rank of card remains the same.

Increasing or decreasing the number of playing cards in a deck is the subject of this article. We’ll explain in depth—with some arithmetic, if necessary—why having fewer decks is preferable.

## More Blackjacks with fewer decks.

One major argument for using fewer decks is that each deck has exactly one thirteenth Aces.

My friend was correct; regardless of the number of decks used, the initial distribution of card values remains constant. Blackjacks are more likely to be dealt when the shoe has fewer cards because each card that is taken out of play has a higher effect.

Probabilities of Getting a Blackjack in a Game With Only One Deck

First, let’s figure out how often a player in a game with one deck will get blackjack. Multiplying the odds of drawing an Ace by the odds of drawing any card with a value of 10 points yields the likelihood of obtaining a blackjack from a shoe containing only one deck. Four Aces and sixteen ten-point cards (four tens, four Jacks, four Queens, and four Kings) make up a standard deck of 52 cards.

This means that the odds of drawing any Ace are 1/13, or 4/52. The odds of drawing a ten-point card after drawing an Ace are 16/51. What do you make of those two digits? Since you’ve already chosen a card, the initial probability, based on a deck of fifty-two cards, no longer applies; instead, you must calculate the likelihood of drawing one of sixteen ten-point cards from a deck of fifty-one.

Because of this shift in the divisor, blackjack players benefit from using fewer decks, while the house’s odds significantly decrease.

Since a blackjack can be achieved with either an initial ten-point card OR an Ace, the true probability of drawing a blackjack from a single-deck shoe must be calculated by doubling the result.

The overall chance of getting a blackjack from a shoe containing only one deck is 4.83%. That’s the product of two times the odds of drawing any ten-point card (16/51) and the odds of drawing an Ace (1/13).

Probabilities of Getting a Blackjack with Two Decks

Let’s have a look at the probability of getting blackjack when using 104 cards instead of 52 to get a feel for the statistical difference between using one and two decks.

The odds of getting an Ace from a two-deck shoe are 8 in 104. If another card is drawn from the same shoe, the odds of it being a ten are 32 to 103. Adding those two numbers together yields 4.78% when multiplied by two.

The probability of getting a blackjack from a single deck of cards is 4.83%. When using two decks, your chances of getting a blackjack are 4.78 percent. The casino has reduced your odds of getting blackjack by 0.05% by adding a deck to the shoe but not altering the rules in any way. Keep in mind that under the normal casino regulations, each of those busted blackjacks would have paid out 3:2. The loss of those 3:2 rewards has a significant effect on both your and the casino’s bottom line.

## Is there a particular reason why fewer decks benefit double downs?

If you’ve been paying attention, you may have guessed that the same factor that increases the likelihood of blackjacks with fewer decks also influences the probability of a successful Double Down. If there are fewer decks in play, doubling down on a hand of 6 and 5 increases the player’s odds of drawing a face card and achieving a 21.

Herein lies the rub: remember that your dealer also gains from these adjustments at lower deck numbers. There are more potential blackjacks for everyone involved, not just the player. Players earn 3:2 for blackjack, whereas the house just gets even money, therefore this fact doesn’t affect the game as much as it might. It’s important to note that the player can Double Down while the dealer cannot. The player has a greater advantage over the dealer thanks to the twofold victory.

## Conclusion

The player has an edge in a blackjack game where fewer decks are used to construct the shoe, assuming all other rules are the same. In particular, I would like to alert blackjack players to the possibility that some casinos may pay as little as 1:1 for a player blackjack when using a single deck. You can get better odds with a single deck, but the casino will only let you play if you agree to pay less for a blackjack. Don’t give in to the temptation of a single-deck game if it pays less than the standard 3:2.