Padma
I have a hard time shuffling my Daniloff, the longest deck I own. I don't have huge hands, but not tiny ones, either...regular size tarot decks are not an issue, but when we are getting to 14 cm's +, forget it!
How big are your hands?
csdude
I don't have a whole lot of experience with multiple decks, but my deck is 5 1/2" (just under 14cm, I guess), and sometimes it's hard to shuffle the entire deck. The fact that I can't quite close my hand around it may lead to sloppy shuffles, possibly causing a misread on a daily draw when I have jumpers.
The thickness of my deck with 78 cards is 1 1/4" (3.175cm). When I'm holding the deck comfortably, the first joint of my middle finger leaves about 1/2" (1.27cm) uncovered. So when I shuffle, the first slice/cut is almost always a thickness of that 1/2", which seems pretty thick.
Because of this, I voted for a rather small 4 1/2" (11.5cm). Even though I can hold a deck that's larger, this size would let the cards fit across two of my middle finger joints instead of just 1.
The thickness of my deck with 78 cards is 1 1/4" (3.175cm). When I'm holding the deck comfortably, the first joint of my middle finger leaves about 1/2" (1.27cm) uncovered. So when I shuffle, the first slice/cut is almost always a thickness of that 1/2", which seems pretty thick.
Because of this, I voted for a rather small 4 1/2" (11.5cm). Even though I can hold a deck that's larger, this size would let the cards fit across two of my middle finger joints instead of just 1.
SarahJoy
Same.
Just for reference, my hands are 20.5 cm from thumb tip to middle finger tip, stretched out on a ruler. I can shuffle all the decks I have.
dancing_moon
My largest deck so far is Feng Shui (13 cm), and it's still a very comfortable shuffle: I can hold it with my middle to little fingers at the top, and I figure there's room for one more cm. In fact, shuffling my larger/heavier decks is a great flexing and strength exercise for my fingers. 
earthair
Functionality wise, I hold between thumb and middle finger+ring finger, pressing down with my index finger to riffle+bridge, so taking into account the cards being bent into a C, the USG and LoS decks of 12cm are the perfect size for my hands to do good controlled shuffling.
Chrystella
I voted 14cm because I have the DruidCraft and I can shuffle them, albeit slowly and somewhat clumsily. It's not just the size of a deck that makes it harder to shuffle for me. Sometimes a deck that is thick is just as uncomfortable. For example, the Flornoy Noblet is small, but it's probably the thickest of all my decks and it has pointy corners (thinking about trimming those). It's a little awkward to shuffle.
gregory
THIS.i need to go see...
...but i also would like to mention, it is not just the SIZE of a deck that makes it difficult to shuffle, but the thickness and/or overly glossiness of a deck.
Schiffer decks are very thick and glossy as an example--and VERY difficult to shuffle...
I don't have big hands but I do know how to use them ! That said, I do prefer to riffle.
My fully spread hand is 20 cm, thumbtip to littlefingertip.
Borrowing TB's descriptions, from the fold in the wrist where the heel of the hand meets my wrist to the tip of my middle finger is 17 cm.
From tip of thumb (open-handed) to tip of middle finger (measured in a straight line) is 16 cm ...
earthair
Personally I think the card stock of Schiffer is fine and I would be able to riffle it into submission in no time at all...if I could just get my hands around them
Riffling is all about releasing the cards in a controlled way off the thumbs, so theoretically card thickness or texture shouldn't be an issue as long as there's a bit of flex in them. And if they're too big to bridge back, then cards end up with a one-way warp.
Riffling is all about releasing the cards in a controlled way off the thumbs, so theoretically card thickness or texture shouldn't be an issue as long as there's a bit of flex in them. And if they're too big to bridge back, then cards end up with a one-way warp.
gregory
I assume you don't have a Mary El ? Or a Sol Invictus... As for the Gorgons... Those ARE rather large even for me, to put it politely (yes, I have the small one now.)Personally I think the card stock of Schiffer is fine and I would be able to riffle it into submission in no time at all...if I could just get my hands around them
The THICK stock is a PIA.
Barleywine
I have the feeling the OP wasn't talking about riffling. If I shuffled by riffling, I could probably shuffle dinner-plate-sized cards. Hand size really has more to do with holding the deck to shuffle it, IMO.
