Your stack size is defined as the amount of chips you have relative to the big blind. What we use in poker, though, is something called your 'effective' stack size, because you can't actually win all of the chips that are on the table. All you can win is the total sum of your chips (if someone has you covered) or the sum of their chips (if you cover them).
Effective stack sizes
Any discussion of stack sizes is going to be made within the confines of what's called effective stack sizes. Consider the following situation:
In this hand, we have 74.5 BB (that's 74.5 times the big blind). Our opponents, though, have less. The opponent with the most chips has just 72 BB. The other players have 66 BB and 52.5 BB respectively. My effective stack size at this table is 72 BB, unless that opponent is folded, in which case my effective stack size is even smaller.
Anytime you're sitting in a poker game, whether you're playing for pennies or hundreds of dollars, you're going to think in terms of stack sizes. Poker is dictated by the size of the stack, relative to the big blind, not the actual dollar value of the chips.
Deep stack vs short stack
We typically divide up stack sizes into rough category estimates:
- Under 20BB: Microstacks
- 20-50BB: Short stacks
- 50BB-125BB: Medium stacks
- 125BB-250BB: Deep stacks
- Over 250BB: Very deep stacks
Because the stack size determines how much money you can make or lose, it's also going to tell you which hands you want to play to make the maximum amount or lose the minimum amount. If you're playing in a game with a small stack size, like 50BB, you're going to play hands that tend to play well in pots that go all in on the flop or the turn. With 50BB, you're going to raise preflop, bet the flop and turn, and you're going to be pretty much all-in by this point. There's not a lot of check-raising or rebluffing or all of these advanced poker techniques because you're playing so short. You can still bluff in short-stack games (and it's often more effective), but you don't have the whole range of motion of your poker arsenal that you would in very deep stack games. In a medium stack game your options open up. You have the option to checkraise and bet the turn and river and get a sizable pot going. When you're playing deep stack, all of your poker options are at your disposal. You can overbet, you can checkraise, you can checkraise as a bluff, you can fourbet and fivebet. This is what it takes to play a very big pot.
When you're playing shorter-stacked poker, you need to value hands like or because those hands have two high cards, and in shortstack poker, high cards are very valuable, because they tend to make top pair. In short stack poker, a top pair is usually good enough to play. If you have top two pair, you're almost always going to get your entire stack in on short stack poker.
When you move into middle stacked poker, the top pair actually becomes dangerous to hold. While big cards do still have value, other cards like , strong suited connectors, also have value, because they make a straight and a flush. That's why in middle-stack poker (where most people play cash games), we prefer hands like to hands like .
In deep stack poker, a hand like actually has some playable value, because it makes a very deceptive nut hand. If the flop comes , you've got the nut straight, and no one will put you on 4-6. In fact, you might win a big pot from A-4.
Thinking about your stack size helps you define what hands you should be playing. You can begin to expand your hand range when you're playing deep stack poker, but in short stack or medium stack poker, you don't have a deep enough stack to capitalize on the upside of playing these weak hands when they do make monsters.
Stack to pot ratio
Your stack to pot ratio is the size of the pot compared to your stack. If your effective stack is 100 BB and, on the flop, there are 20 chips in the pot, your SPR is 5. SPRs tend to run between 1 and 30. A SPR of 30 means we're very deep relative to the pot. An SPR of 1 means we've got exactly the same amount as the pot left in our stack. With an SPR of between 0 and 7, we love playing hands like top pair, because we're going to bet two streets and be all in. With an SPR between 7 and 14, we're deeper and will start to value hands like draws more than top pairs. With an SPR over 20, you're you can play a lot more hands before the flop. You need an SPR over 25 to consider playing a pocket pair in order to flop a set.
The SPR is not just a passive measure - it's something we can actively engineer through our raise sizing. If our effective stacks are 100 BB, and we want to build an SPR under 7 for a hand like , we need to raise so that, if anyone calls us, the pot will be at least 15 BB. Typically, we might raise 3 BB before the flop, but since one caller will only leave 6 or 7 BB in the pot, we should opt to raise more like 6BB here in order to get ourselves as close to that SPR number as possible. Even if it prices some players out of the pot preflop who would have called, they might have actually been correct to call if we gave them the correct pot odds before the flop. On the other hand, if I have 300BB deep, I want to keep the SPR as high as possible, somewhere near 30. To do that, I'd just want 10BB to be in the pot on the flop. If someone has already raised, I might opt to call. If no one has raised, I will min-raise or raise three-times the big blind in order to keep the pot at a managable size. This will allow me to put the maximum amount of chips in the pot once I do flop my hand.