Stack-to-Pot Ratio & M-Ratio Calculator
M tells you how many orbits folding buys. SPR tells you the exact equity a stack-off needs. Both computed, with the identity behind them shown.
M — how long folding lasts
SPR — what it costs to get it all in
All of it from one identity: at an SPR of S you put S pots in to win a pot of 1 + 2S, so you break even at S ÷ (1 + 2S). The bands people memorise are what that curve looks like.
Pot odds
When the blinds catch up with you
This assumes your stack never changes, which it will. It is not a prediction — it is the clock the structure is running on you if you sit still.
The zones
What these ratios do and do not tell you
- M is not a band to memorise — it is a count. An M of 8 means eight orbits of folding before the blinds have taken everything, and that is the definition rather than a rule of thumb built on top of it.
- Effective M matters more than M at a short table. Nine-handed you pay the blinds once every nine hands; three-handed once every three, so the same stack is worth a third as much time. The zone you are actually in is the effective one.
- The SPR bands people memorise are a consequence of one identity, not a table. At an SPR of S the break-even equity for getting all the chips in is S divided by (1 + 2S): a third at an SPR of 1, 44% at 4, 48% at 13, and never quite a half however deep you get.
- That identity is why low SPR lets you commit with top pair and high SPR does not. Nothing about the hand changed — the price of the stack-off did. Deciding which one you are in belongs before the flop, when you choose the size of the last bet.
- Pot odds and equity are the same statement twice. Calling a bet that makes the pot four times your call needs 25% to break even, and the number does not care what your hand is; it only tells you what your hand has to be worth.
- None of this prices a bubble. Every figure here is in chips, and a chip near a pay jump is not worth what a chip is worth on the first hand — which is the one adjustment no ratio on this page will make for you.
How to use
- Enter your stack and the blinds to get your M and zone.
- Enter the flop pot and effective stack to get your SPR.
- Read the equity a stack-off needs before you build the pot, not after.
Frequently asked questions
What does M actually mean?
It is a count, not a band. An M of 8 means eight full orbits of folding before the blinds and antes have taken your whole stack — that is the definition, and this tool checks it by paying the blinds one orbit at a time rather than by trusting the formula. Nine-handed, an M of 8 is 72 hands.
Why does effective M matter more than M?
Because a short table charges you the blinds far more often. Nine-handed you post once every nine hands; three-handed once every three, so the same stack buys a third as much time. Effective M scales your figure back to a ten-handed reference, and the zone you are really in is that one.
What equity do I need to get all the chips in?
Exactly the stack-to-pot ratio divided by one plus twice it. At an SPR of 1 that is 33.3%, at 4 it is 44.4%, at 13 it is 48.1%, and it approaches half without ever reaching it. Every SPR band you have been told to memorise is just a point on that curve.
Why does low SPR let me commit with top pair?
Because the price of the stack-off changed, not the hand. At an SPR of 1 you are risking one pot to win two, so a third of the time is enough and top pair clears that against nearly any range. At an SPR of 13 you need almost half, which one pair simply does not have.
When is the SPR decided?
Before the flop, when the last pre-flop bet sets the size of the pot relative to what is behind. By the time you are staring at a flop the number is fixed and all you can do is read it. That is why pot-size control is a pre-flop skill rather than a post-flop one.
Are the zone names official?
They are Harrington’s, from Harrington on Hold’em, and they are quoted as the published scheme they are. Everything numerical on this page — the orbits, the hands, the equity requirements, the level-by-level forecast — is computed rather than recalled.
Does this account for the bubble?
No, and that is the one gap worth knowing about. Every figure here is in chips, and a chip near a pay jump is not worth what a chip is worth on the first hand. No ratio on this page makes that adjustment for you — it is the thing you have to bring yourself.
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