Average stack size is the mean. It is usually well ahead of the median (although top 20-25% is unusual - it's usually 35%). Do with that information what you will. The Q-ratio (also known as Q number or just Q) is used in poker tournament strategy. It is also known as the 'weak force.' The Q-ratio describes the relation of the player's stack to the tournament players' average stack. A low Q-ratio — less than 1 — indicates a below-average chip stack, implying disadvantage against opponents.

This article was written by blackrain79.com contributor Ryan Lewis.
There are all sorts of mathematical equations that can be utilised in poker to assist players to help with their decision making in game.
In order to become successful long term players, we must have a good understanding of poker math theory so it can be applied in real time during live or online play.
Although not the most sexiest subject in the game, a lack of understanding in basic math can lead to costly errors down the track and force our win rate or return on investment to take a substantial hit.
In this article I will introduce the stack to pot ratio equation and how you can use it in game to boost your win rate and results.

What is the stack to pot ratio?

The stack to pot ratio (SPR) is a simple basic calculation that tells us how much we are willing to risk to win a hand.
The equation is calculated post flop and applies on the flop only and before any betting is done. The formula is:
For example, we head to the flop as the pre flop raiser and only the big blind calls. The pot size is 6.5BB. I have 97BB in my stack, the big blind has 40BB in theirs.
The effective stack is 40BB, as I can only win what the big blind has remaining. The stack to pot ratio is: 6.2
6.2 = 40 / 6.5
Depending on what blog you read or what poker book you have, you will find that there is conflicting information on what a low, medium and high SPR is. Some books will say that a low SPR is 2.5, others will say 3-4, and then others will say 6.
As per usual in life the answer lies somewhere in the middle.
Through experience of playing hundreds of thousands of hands I have come up with my own conclusions on optimal stack to pot ratio numbers:

• Low SPR: < 4
• Middle SPR: 4-10
• High SPR: > 10

How to interpret the stack to pot ratio

By calculating the SPR we can make a logical decision if we want to play for all the money on the flop.
Below is a hand strength guide which we can use to determine how willing we are to play for all the money on the flop based on the stack to pot ratio:
The basic premise is the higher our SPR is, the higher our hand strength must be to auto stack off on the flop. Overpairs also do well in SPR’s of 6 and below.
Bare also in mind that these numbers are fluid. If you have a specific read on villain and know they like to stack off light, then getting it in with top pair when the SPR is 6 is viable.
Another point to keep in mind is 3bet pots usually create an SPR of roughly 4. This allows you to stack off comfortably with top pair and overpair type holdings.
Draws can be tricky to play with middling SPRs because you can be forced to call it off on the flop if you are presented with the right pot odds.
This can happen if you check raise the flop from the big blind with the nut flush draw and then face a jam. If presented with correct pot odds I advise to make the call, even if the SPR suggests otherwise.

Examples of using the stack to pot ratio

Alright, let's look at a few different examples of using stack to pot ratio in poker. Hopefully this will give you a better understanding of how to use SPR at the tables yourself.

Low SPR example

Button (Hero) 100BB vs BB (villain) 26BB
We hold A♠ K♣
Flop
4♠ 8♦ A♥
Pot is 6.5BB, SPR is 4. Villain donks for 3BB.
Hero should raise to 9BB and look to call a jam from the BB.
This is an easy stack off opportunity on the flop. We flop top pair top kicker in a low SPR of 4.

Middle SPR example

Button (Hero) 100BB vs BB (villain) 50BB
We hold 4♥ 4♣
Flop
4♠ 6♦ 7♦
Pot is 6.5BB, SPR is 7.7. Hero cbets 4BB. Villain check raises to 12BB.
Hero should jam.
Here the SPR is a little higher at 7.7. We flop bottom set and face a check raise on a wet board.
On this flop we should look to get it in immediately as there are many cards on the turn and river that will kill the action.
Any diamond, 3, 5, 8, 9 and T (almost half the deck!) are bad cards for us and we would rather get our money in on the flop when we are ahead the majority of the time.

High SPR example

Button (Hero) 100BB vs BB (villain) 100BB
We hold A♠ A♥
Flop
8♠ 8♥ 5♥
Pot is 6.5BB, SPR is 15.4. Hero cbets 2.5BB. Villain check raises to 10BB.
Hero should call.
In this example the SPR is high at 15.3. Our threshold for stacking off on the flop at this level should not be overpairs. Hero should call and reassess the action on the turn.

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How the stack to pot ratio can help your poker win rate

Here are a few concepts we can use both pre flop and post flop to assist us in how we plan a hand. First we need to take note of our opponents' stack sizes.
One of the most important and underrated skills we can undertake is to be more aware of our opponents stack size when heading to the flop.
Once we have a rough idea of the SPR, we can plan accordingly and decide whether we want to play for all the money before we perform our action.
You should have a rough idea of the SPR in every hand you play.
We can also exploitatively fold and not cold call marginal holdings such as low pocket pairs and suited connectors pre flop when facing an open raise from a short stacked player (60BB or less).
These holdings perform best with SPRs of 10 and higher.
The logic here is that you need to have the opportunity to win a large pot to balance out all the times when you call a raise and are forced to fold when you miss.
This is something that Phil Ivey talks about in a lot more detail in his recent MasterClass poker training.

Tailor your preflop bet sizing to your preferred stack to pot ratio

This situation will occur usually when we face opponents who open limp with a short stack. The general advice is to isolate the limper by raising to 4BB if you have a hand worth playing.
I would add to this advice that you can and should exploitatively raise larger to at least 6BB (or sometimes higher) when you hold a high pocket pair.
The limper will still call the majority of the time and by raising larger you create a larger pot heading to the flop which creates a smaller stack to pot ratio.
Smaller SPRs benefit big overpairs as you can easily get it in on the flop if facing aggression. By the way, I have already written the complete guide on when to fold your overpair.
We can also use this advice when 3 betting. Instead of 3 betting to a conventional 9 or 10BB we can opt for a larger sizing, such as 11 or 12BB.
If our 3bet is called we often head to the flop with an SPR of under 4 (assuming we are playing for 100BB), which can make our decisions easier if we decide to play for all the money.
I would advise against opening the pot (meaning we raise first in before any limpers) pre flop to a sizing higher than 3BB.
Even though this creates a smaller SPR, it forces your opponents to play perfectly against you by calling tighter and 3betting hands that have you crushed.
Unless there are major whales at your table, your raise first in size should be between 2.5-3BB. Remember we make money in poker from our opponents mistakes, not by forcing them to play well.

Proceed with caution when playing deep stacked

There is no worse feeling in poker than accumulating a 200BB stack, only to lose it all after overvaluing an overpair or the low end straight. Or having to think about folding bottom set on the flop when the SPR is 30.
Personally I hate playing deep stacked and to this day I avoid it like the plague. I make a conscious effort to reload the table once my stack is 150BB or higher.
I prefer to keep my decisions as simple as possible at the table and I achieve this by sticking to a stack size of around 100-150BB.

Poker Average Stack Game

I'm not saying that you should do this as well but mastering how to play one stack size is superior than being average at short, regular or deep stacked.
If you stick to one stack size then you get used to what the SPR’s will be and your post flop decisions will become much easier.
If you find yourself playing deep stacked for 200BB often then be aware that the SPR will be between 25 and 30 routinely.
That means your threshold for stacking off on the flop should in theory be much higher and will be narrowed down to middle and top set, and nutted flushes and straights.
For much more on playing optimal deep stacked poker (and how to use SPR when super deep), check out the The Upswing Poker Lab.

Final thoughts

The stack to pot ratio is a simple math calculation we can utilise on the flop to decide how willing we are to risk our stack to win the hand.

Poker Average Stack Games

The higher the SPR is on the flop, the higher our threshold and hand strength will be for getting all the money in.
Try and make a habit to know what the SPR is every hand you play so you know how to proceed on the flop if you face aggression.
In doing so it will allow more clarity in our post flop decision making process.
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This article was written by Ryan Lewis. Ryan specializes in 6max cash small stakes online poker. He focuses on playing a fundamentally strong tight and aggressive strategy. He particularly enjoys the statistics and game theory side of the game. You can follow him on Twitter right here.
Let me know your thoughts in the comments below on stack to pot ratio. Do you use stack to pot ratio at the poker tables to improve your decision making?