How many times do you really need to shuffle?

For a 40-card Spanish deck, around six or seven riffle shuffles — splitting the deck and interleaving the two halves — work well. The benchmark comes from mathematicians Dave Bayer and Persi Diaconis, who calculated in 1992 that it takes around seven shuffles of this kind to thoroughly mix a 52-card deck.

The seven-shuffle study

Bayer and Diaconis studied how closely a deck’s order resembles its starting order after each shuffle. After just a few shuffles, traces of the original order remain. From around seven onwards, the deck is almost as mixed as if its cards had been arranged at random. Further shuffles make very little difference.

Not all shuffles are equally effective

The overhand shuffle, where you pass small packets of cards from one hand to the other, is the most common method in Spain, but it mixes the cards much less thoroughly. It would take many more shuffles to achieve the same result. That’s why it’s worth combining methods. You’ll find the details in how to shuffle cards properly.

Why it matters

In games such as Chinchón (a rummy-style game), if you don’t shuffle properly, cards from the previous hand tend to come out together: three-of-a-kind sets and runs that were already formed. This creates odd advantages and makes games less fair.

What about online?

Digital decks are shuffled using algorithms that produce a fully random order for each deal, with no traces of the previous hand. If you’d like to know how many possible orders there are, read how many combinations a deck of cards has.