Blackjack Single Deck is Better

by Henry Tamburin

Why is a blackjack single deck game better for the player than a multiple deck game?
This lesson at Learn to Play Blackjack answers that question.
One of the major reasons is simply due to the fact that you will be dealt more hands in a blackjack single deck game compared to a multiple deck game. Here's why this is so.

Suppose you took a single deck of cards, shuffled them, and then randomly picked one card. What is the probability that you'll pick an ace? Since there are four aces in a single deck of cards, the chance of drawing one of those aces is the ratio of 4 over 52. 
Once you draw the ace, you are left with 51 cards to draw a ten-value card. 
There are 16 ten-value cards in a deck of cards (the four tens, jacks, queens and kings) so the chance of drawing one is the ratio of 16 over 51. If you multiply these two ratios, you will compute the probability of getting an ace followed by a ten-value card in a single deck to be 2.41%. (4/52 times 16/51 = 2.41%.)

However, you could have just as easily drawn the ten-value card first then the ace. Therefore, the overall probability of getting a BJack hand in a single deck game is twice 2.415 or 4.82%.
This translates into one out of every 20.72 hands, an important statistic.

For a 6-deck game the chance of drawing the ace as the first card is the ratio 24 over 312. The chance of drawing the ten-value as the second card is the ratio 96 over 311. Multiply the two ratios and you get 2.37%. Double it and you get 4.74%, which is, less than the 4.82% probability of getting a BJack in a single deck game.
In fact, if you do the math for 2, 4 and 8 decks here is what you'll calculate as the probability of getting a BJack hand.
Single deck=1 in every 20.72 hands
Double deck=1 in every 20.93 hands
Four decks=1 in every 21.02 hands
Six decks=1 in every 21.07 hands
Eight decks=1 in every 21.07 hands
Notice that you'll only be 98% as successful at drawing a BJack in an eight-deck game compared to a single deck game, which makes the blackjack single deck game better.
Essentially the effect of removing a card from a single deck affects the percentages of the remaining cards to a much greater extent than in a multiple deck game. This is another important point to remember when you playing blackjack single deck.

Although getting more BJacks is good for the player, it's even better when you get one and the dealer doesn't. Which brings me to the second reason why the blackjack single deck game is better than a multiple deck game, namely the dealer’s chances of duplicating a BJack is less in a single deck game compared to a multiple deck game.
The exact probabilities of the dealer duplicating our BJack in the same round are:
Single deck =1 in every 27.25 hands
Two decks=1 in every 23.74 hands
Four decks=1 in every 22.34 hands
Six decks=1 in every 21.92 hands
Eight decks=1 in every 21.71 hands
BJack pushes are about 20% more likely in a six or eight deck game, compared to a single deck game, which reduces our earnings potential (remember you get paid 3 to 2 on a BJack hand when the dealer doesn't have BJack but gets nothing when he does have a BJack).
This makes a blackjack single deck game a much better game.
Another reason that a player's expectation is better in a single deck game is that a player is more likely to get a good hit when doubling down on 10 or 11 compared to the same situation in a multiple deck game.
When you get a 10 or 11, it's usually made up of two undesirable small cards. Their removal from the single deck increases our chances of getting a good hit.
Because of the dilution effect of so many more cards in multiple deck games, the probability of drawing a good card is less compared to the single deck game.
To summarize, single deck games are a better deal for players because:
1. You will be dealt more BJack hands
2. The dealer is less likely to also have a BJack hand and tie you, and
3. You are more likely to draw a good card when you double down on 10 or 11.
Even though single deck games have historically been better for players than multiple deck games, don’t run to your favorite casino and sit down at any old single deck table.
Check first what the house pays for a BJack because many casinos nowadays are paying only 6 to 5 rather than the traditional 3 to 2.
The 6 to 5 payoff is terrible and increases the house edge to over 1% against a basic strategy player.
Therefore, single deck games are good but only when the house pays 3 to 2.

Blackjack Single Deck is followed by a lesson about Surrender
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