Why Single Deck Games are Better
Why is a single deck game better for the player than a multiple deck game? I must get asked that question at least once a day because the reason isn't very obvious to most blackjack players. But one of the major reasons is simply due to the fact that you will be dealt more blackjack hands in a 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 blackjack hand in a single deck game is twice 2.415 or 4.82%. This translates into one blackjack out of every 20.72 hands, an important statistic in blackjack.
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 blackjack 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 blackjack 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 blackjack in an eight-deck game compared to a single deck game, which makes the 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.
Although getting more blackjacks is good for the player, it's even better when you get a blackjack and the dealer doesn't. Which brings me to the second reason why the single deck game is better than a multiple deck game, namely the dealer chances of duplicating a blackjack is less in a single deck game compared to a multiple deck game. The exact probabilities of the dealer duplicating our blackjack 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
Blackjack 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 blackjack hand when the dealer doesn't have blackjack but get nothing when he does have a blackjack). This makes a single deck game a much better game.
Another reason that a player's expectation is better in a single deck game is that he 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 the major reasons why the single deck game is better than a multiple deck game for the blackjack player is:
You will be dealt more blackjack hands
The dealer is less likely to also have a blackjack hand and tie you, and
You are more likely to draw a good card when you double down on 10 or 11.
Given a choice, opt for the single deck blackjack game over the multiple deck game.