I recently finished reading through PNLHE by Ed miller et al and decided to make a few quick charts in excel to better understand the concept, to share it with you all, and to start some discussion on this concept. I believe it to be pretty important, but in the book the theoretical reasoning behind it is kind of taken for granted. If you are unfamiliar with SPR it stands for stack to pot ratio; it is essentially a measure of how much bigger the remaining stack sizes are compared to the preflop pot. So if you have an SPR of 10 then to go all in you must put in 10 times the amount of the pot preflop.
To start off this is the quick spreadsheet I threw together. The first chart gives the size in big blinds of the preflop pot for 1, 2, and 3 callers(along the top) for various sizes of preflop raises in bb(vertically). Immediately to the right SPR is calculated using the starting stack size(given as 100bb) and the data in the first chart. One interesting thing to note is that with 1 caller and the standard so-called preflop raise of 3bb you pretty much hit the dreaded SPR of 13 for 100bb starting stacks.(but 3 betting and bringing it to 8bb+ gives you a perfect spr for your tptk type hands)
The other two charts are used to calculate the money in the pot and the money put in the pot when compared to the preflop pot size assuming you bet a standard size every pot and one caller. This obviously isnt the case in real life, but it gives you an idea of how SPR is brought into action.
I bring in a term Total preflop pots or (TPFP) to describe the amount of preflop pots you have put in so far. For instance, shown is a bet sizing of .75 of the pot per bet. So say you bet and get called flop, turn, and river. Flop you are betting .75 times the pre flop pot size(P) making the pot size 2.50P. On the turn you bet .75 the pot size, making the bet 1.88P creating a 6.25P pot. You have now put in 2.63*P.
Another ratio I have there is TPFP/SPR and adj TPFP/SPR. This basically always is less than or equal to 1. When you hit 1 you are all in. This also relates to commitment and the commitment threshold. The adjusted TPFP/SPR adjusts this ratio assuming you put in .5P in preflop(which isnt the case unless you are sb and bb, but it really doesnt matter in no limit). These values are also more or less the same adjusted or unadjusted. Esesntially when you hit around .1 you need to make your commitment decision and at .33 you are commited; the next pot sized bet puts you all in.
The last chart gives the TPFP for various bet sizes, basically showing you that you are missing out if you bet small. If you are going to bet one of these sizes this essentially gives you the SPR you need to get all in the given number of bets. If you bet 2/3rds pot you need an SPR of 5.75 to get your stacks in on the third bet.
I hope you got something out of this, and all though much of this may be trivial it is very easy to not put in the effort to understand what you are doing and why it is good for you. If you see any mistakes or if I am completely full of **** please let me know.