Introduction to ‘Stack-to-Pot Ratio’ (SPR)
Stack to Pot Ratio, or SPR for short, is a tool for helping to plan your hand around commitment decisions. In short, by providing a quick, easy framework for relating the size of the pot to the remaining effective stacks, you’ll be able to more easily determine if your hand strength warrants playing an all in pot or not.
SPR is easy to calculate. It’s the ratio of the size of the pot, to the size of the effective stack (chips still left to bet). So if there is $50 in the pot, and $100 left to bet, the stack to pot ratio is 2 (100/50). The important thing to remember is that SPR is calculated by the effective stack. If we had $2000 in the example, but our opponent only had $100, then the SPR with them is 2 since $100 is the most we can bet before they are all in. It is also possible to have different SPR’s with different opponents in multiway pots. If there was a 3rd player in the above hand, who, like ourselves, also had $2000 left to bet, then the SPR with the short stack player is still 2, but our SPR with the third player is 40 (2000/50). We would be willing and profitable to play many hand strengths all in vs. the short stack that would not be profitable to play all in vs. the other big stack.
As a basic example of extremes to help illustrate, suppose you have AhAd and the flop comes KsTc3d. Are you willing to get all in on the flop? If the pot contained $10 and the effective stacks had $1000 behind to bet (SPR of 100), getting all the money in would be rather insane and a losing play, because no one in their right mind will put 1K more in the middle in a $10 pot with a hand that can’t beat 1 pair. If, however, the pot contained $1000 and you had $10 left to bet (it’s an exaggerated hypothetical, bear with me here), of course you’d put that last $10 in. You would even put the last $10 in without a connection to the board… not only because you have a correct price to draw to anything, but you may have the best hand right now with something like ace high or king high as your opponent will eagerly (and correctly) put the last $10 in with any 2 cards and 1K already in the pot.
The lower the stack to pot ratio, the larger the pot is relative to what’s left to bet. Thus, opponents will be getting a better price to play for the rest and should be willing to do so with lessor holdings. While the example above was made with extremes, it should be clear that this is the basic logic of SPR.
One of the ways we can use this tool is to understand what kind of SPR we might have on the flop that will allow a player to get all in on the river with reasonable sizings. For example, if the stack to pot ratio on the flop is 13, it will take exactly 3 pot sized bets to be all in on the river. We can see this if we walk through the betting each street as follows:
Pot size = P
Effective Stack = 13P (SPR = 13)
If we bet 1P on the flop and are called, there will be 3P total going to the turn, and we’ll have 12P left to bet. On the turn we pot it again betting 3P and are called again. Now there is 9P in the pot, and 9P left to bet for a pot sized river all in.
You can work through a similar process for various effective stack sizes, and bet sizes. Let’s conclude with some general (not written in stone) guidelines for certain flop SPRs and willingness to play for all the marbles:
SPR 4 or less: This low SPR on the flop is one where we should feel comfortable getting our stack in with strong 1 pair hands. It will only take 2 pot sized bets to get all in, or 3 smaller sizings, and most players will have a hard time folding their pairs, particularly their better ones, in this sequence.
SPR 10 or more: The higher SPR’s make it precarious to get stacks with one pair hands. The more money there is to bet relative to the pot, the less likely an opponent will be to put it all in the middle without a very strong hand.
SPR 4 to 10: These middle of the road stack to pot ratios on the flop can go either way. Take the AhAd and the flop comes KsTc3d example from above. If our opponent were a known calling station, we can feel very comfortable getting in across 3 streets even on an SPR of 10, because stations will pay us off with many worse one pair hands. If our opponent were a very tight, conservative player however, we may not be retaining much edge getting all the money in on an spr of 5, because that opponent type is loath to play for stacks without very strong hands. What if you have no reads? In micro stakes, it’s safe to err on the side of assuming players will call too loose and too often, and be willing to go for the value with your strong one pair hands at a bit higher spr’s.
The basic premise of stack to pot ratios is simple… the larger the stacks relative to the pot, the stronger a hand we need to be willing to stack it all off. And when the money left to bet is shallow relative to the size of the pot, we should be reluctant to give up on that (relatively) large pot and willing to get in much lighter.
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