Why Does The Number of Decks Matter in Blackjack?

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Fewer Decks are Better. Do You Know Why?

When it comes to the number of decks in a blackjack game, the fewer the better. Most players have heard this fact somewhere along the line, but many of them don’t know why fewer is better.

I often get this question by email, where players will note that the proportion of each rank of card is the same whether the casino uses a single deck or shuffles six decks together. Regardless of how many decks are in play, we start out with one thirteenth of the cards being Aces…

You Get More Blackjacks in Games With Fewer Decks

Despite the initial card proportions being equal, in games with fewer decks you will be dealt more blackjacks. You will also be more successful in your double downs. How can that be, when all the ranks are equally represented no matter how many decks are used? It is because removing cards has more impact in a game with fewer decks.

How Often Will You Draw a Blackjack From a Single Deck?

To get the probability of drawing a blackjack from a single deck, we multiply the chance of drawing an Ace by the chance of drawing a ten-value card. In a single deck of 52 cards there are 4 Aces and 16 ten-valued cards (4 each of Ten, Jack, Queen, and King).

p(Ace) = 4/52 = 1/13
p(Ten) = 16/51

Note that the second line reduces the number of cards in the divisor to 51, to account for the removed Ace. And that’s where the difference lies.

We also need to double the result since we could draw either (Ace,Ten) or (Ten,Ace). Our final result is:
p(Blackjack) = p(Ace) * p(Ten) * 2 = (1/13) * (16/51) * 2 = 4.83%

The probability of drawing a blackjack from a single deck is 4.83%.

How Often Will You Draw a Blackjack From Two Decks

Same idea with two decks, with different numbers. 104 total cards, including 8 Aces and 32 ten-value cards…

p(Blackjack) = 8/104 * 32/103 * 2 = 4.78%.

The probability of drawing a blackjack from two decks is 4.78%.

More decks means slightly fewer blackjacks. In six decks, the probability drops further yet to 4.75%.

Double Downs Work Better in Fewer Decks Too

The same effect impacts double downs. If you double your initial hand of (6,5) for a total of 11, then you are slightly more likely to draw a face card to make 21 if the game uses fewer decks.

Astute readers may notice that the dealer gets the benefit of these changes as well. That’s right, the dealer gets more blackjacks in single deck, and the dealer draws to 21 more often just like the player. But note that a player wins 3:2 for blackjack, while the dealer gets only even money. And for hands like the double down example, the player wins twice the initial bet. So while both player and dealer get more of these good hands, the player is rewarded more handsomely for his.

But You Get Fewer Pat 20s in Fewer Decks!

It’s not all good news with less decks. For the same reason, you will get fewer dealt hands of 20! Once you remove the first ten-value card, there are only 15 tens left in 51 cards in single deck, while in double deck your chances are better with 31 out of 103.

This impact of fewer pat 20s affects players and dealers equally, so it’s really a wash.

The bottom line is that, all other things being equal, you should play in games with fewer decks. Just make sure they pay 3:2 on blackjack!

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Frank Petolino
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Frank Petolino

I have been asking this question. How many blackjacks can be made in an 8 deck shoe?

Frank Petolino
Guest
Frank Petolino

Does anyone have an answer. I have gotten from 32 to 512. I feel the answer is 128. Does anyone have the right answer. This has been going back and fort with a few people for several days and can’t believe the answers I’m getting. Please respond. Thanks

Anon
Guest
Anon

Not complicated. There are 4 Aces per deck, times 8 decks. That’s 32 possible blackjacks.

Frank Petolino
Guest
Frank Petolino

4 aces x 4 (10)=16 per deck. So 8 decks x 16= 128. So again is that correct or not. Some people have come as high as 512.

Frank Petolino
Guest
Frank Petolino

Don’t think that’s correct. Just one deck. 4 Aces and 4 Tens (picture cards + 10) =16 different ways to get 21.

Frank Petolino
Guest
Frank Petolino

Wrong.

Anon
Guest
Anon

Are you asking how many can be dealt from one shoe, or how many distinct ways to make blackjack (which would not depend on the number of decks)?
This seems pointless and stupid regardless. It’s not rocket science.

Frank Petolino
Guest
Frank Petolino

It was not my question but one given to me. Yes from one shoe how many ways.

Anon
Guest
Anon

Yet again you pose your question in a way that could mean multiple things. This will be my final reply regardless if you like my answers. A) I don’t think this version is your question, but just in case: If you want to know how many blackjacks can be dealt from one 8 deck shoe, I already gave you that answer. It’s 32, because every blackjack requires an Ace, and there are only 32 Aces in an 8 deck shoe. B) How many different forms of blackjack can be dealt? The answer is the same regardless of how many decks… Read more »

LV Bear
Editor

Anon is correct at 32.

Anonymous
Guest
Anonymous

Why oh Why would you boys and girls play online Blackjack, do you need to punish yourself?

chinga ching ching
Guest
chinga ching ching

all chinese are crooked…never trust a chinamen…

Johnny Clueless
Guest
Johnny Clueless

Sorry to contradict your dream of winning a house . In Philippines ,they don’t just use 6 decks but all use CSM !!

Gamblers Pro
Guest

Thanks for clearing this up!

I play a lot here in The Philippines where I’m living, and I’ve noticed the casinos here are all using 6 decks. I’d always wondered why, and now I know.

My grandad won his house in a game of blackjack in the 80’s (yes, I’m serious), and I’ve always had a love for the game since I started playing. Let’s hope I can win a house, too 😀

irreconcilable mathematician
Guest
irreconcilable mathematician

Actually, the lower the number of decks, not necessarily the better. Though if you’re lazy, it’s more appealing. It depends on 3 things – how many decks are in the shoe, where the cutcard is, and what the minimum bet is. In most places I have been, in the pacific northwest and in Indian casinos in the midwest of the US, there are 2 games you’ll see standard. The 2 deck game and the 6 deck game. Typically, the cut card will be one deck before the end in EITHER ONE. Which means that in the 6 deck game, you’ll… Read more »

irreconcilable mathematician
Guest
irreconcilable mathematician

Oops. Correction – the VARIANCE is the function that has the parabola, not the standard deviation. So the 3 points that define the parabola are x=0 and y=0, x=52*(number of decks in show) and y=0, and x=1 and y=12/13. The STANDARD DEVIATION of the count after the first card has been dealt is sqrt(12/13), the variance of the count after the first card is dealt is 12/13.

Mark Wheeler
Guest
Mark Wheeler

It’s now 10/5/16 PM(Pre-Matthew) and it’s not fixed at all. The recommended casinos pop-up hides the free game! I’m not a competent computer programer, but surely you could find one. Wheelmarks

Tum
Admin

Hi Mark,

We’ve narrowed down the issue and it shouldn’t be happening anymore. Thank you for your patience and my apologies for any inconvenience caused.

Cheers,
Tim

jacky
Guest
jacky

they are doing a promotion of an UNLIMITED 1% deposit rebate and that means if you play single deck game with a house edge of 0.3%,you will end up with a player edge of 0.7%.Now I know what “when its too good to be true,it probably is” means.

Jesse
Guest
Jesse

Its simple…. you are prob playing a game with even money black jack

jacky
Guest
jacky

i would love anyone who saw my post to share it with other players in other casino forums.Even if you think i am just a paranoid soar loser who got pissed by nothing but simply regular bad luck,at least get this information talked about and debated on so as to either prove me wrong or warn others. If any Chinese blackjack players can see this,Please be cautious ever after or PM me if you have anything else related you would like to share with me(中国的朋友看过来!)

jacky
Guest
jacky

there is a rogue casino i felt much obliged to report: the www_188bet_com——-Chinese version. According to them,they are legally regulated and licensed by the Isle of Man,which,as most of us know, is one of the most reputable gambling regulation authority.However,there is something odd about this.when you enter the webpage of its “table games”,the little icon of Isle of Man at the bottom of the main page suddenly turns into the icon of First Cagayan.I shared with them this confusion I had and they gave no explanation. When I play their microgaming single deck black,something even weirder happened.I won in a… Read more »

Him
Guest
Him

I played live one night. Lost 20k, bout 73% of the cards were 7 or lower so every time i doubled i would get a 2 or 3 45% of the time at almost even time, so i ADJUSTED!! I stopped Doubling, keep hitting the 10 or 11 n get to 21 the hard way but I watched 32 cards come out n only 3 pictures, right!?.. Wasnt mad that i lost, but watched the next 60 cards come out, n told the dealer to watch with me., 8 picture cards came out, he started shaking his head i jus… Read more »

Anonymous
Guest
Anonymous

Yo guy i absoloutely agree with you 100% Weather it’s 20k or 2 k It’s nothing to beat me fair and square But to cheat me???? I just left the casino Out of Four tables Everyone of the tables first card Was a face a ten a seven or an ace They just cheated me out of 2k today I bet a $600 dollar hand and bet $25 on lucky ladies The dealer delt me a 20 Two jacks So she paid the hundred from betting $25 On lucky ladies Her turn up card was a face And the turn… Read more »

Anonymous
Guest
Anonymous

I was told by a casino dealer in Vegas that those ShuffleMaster machines shuffle the cards Numericly ! Hmm, Food for thought. Any reaction are appreciated. Thanks

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