As the name suggests Stack to Pot Ratio (SPR) is a measure of how big your stack is relative to the pot. We use it as a way to determine how committed to you should be to the pot.
The SPR formula is simply:
Effective Stack Size/Pot Size = Stack to Pot Ratio
When your SPR is low, you should be prepared to commit with medium strength hands, when it is high you should be committing with the top end of your range. Unless of course you have a reliable read which suggests otherwise.
Let’s use a couple of examples to illustrate this.
The pot is $100 and you have $150 left in your stack (it could be a 4-bet pot, for example). You have AJ
The flop is J98.
Your SPR is:
$150/$100 = 1.5 SPR
In a spot like this you have to be prepared to stack off with top pair top kicker. You have committed too much money relative to your stack size not to. The low SPR of 1.5 makes it easier for you to get your money in the middle. You could easily get action from a worse Jack, a worse pair, a heart draw or AK/AQ here when pot size is so small relative to the effective stacks.
When SPR is high
But what if we have the same hand and flop, but this time we have a stack of $195 and the pot is $10?
The SPR this time is:
$195/$10 = 19.5 SPR
Now stacking off with top pair could be a disaster unless you have a huge read on your opponent. If, for example, you bet and get reraised all-in on this flop you realistically are only beating a drawing hand and even that would win a lot of the time. You likely are up against an overpair, two pair, a set, a straight or a dominating combo draw if you get that much action. The SPR of 19.5 is a warning sign that you need a very strong hand here to commit a lot of chips to the pot.
It’s very situational and depends on your opponents, but when the SPR is 0-3 you should be prepared to stack off with one pair type hands and when it is higher than 6 you should be proceeding with caution unless you have sets or better. Anything between is a judgement call.
Before you start over committing to every pot you find yourself in with a low SPR a few warnings. First of all this doesn’t mean you should be 4-betting preflop with junk to justify stacking off with third pair post flop because the SPR said you should. You can orchestrate unprofitable situations preflop even if the post flop spot is technically profitable.
Secondly, SPR naturally gets lower with each street in Hold’em, when you put money in on the flop your SPR will be lower on the turn. This doesn’t mean you should be stacking off with weaker hands on the turn than you would the flop, this is where the Funnel Principle comes in to play.
Intro to SPR
Tackleberry with the lowdown on Stack to Pot Ratio
LuckyLukePS with a guide to betting in poker tournaments