Stack depth refers to the amount of chips remaining in a player's stack.
Effective stack
When two players are in a hand, the only stack size that matters is the smaller of the two. This is called the effective stack and represents how many chips can be won or lost in the hand.
Stack-to-pot ratio (SPR)
SPR is the ratio between the effective stack and the pot size. SPR is a planning tool that helps players understand how much room they have to maneuver in a hand.
SPR = effective stack / pot size
| Spot | Effective Stack | Pot | SPR |
|---|---|---|---|
| BTN vs. BB single-raised pot | 97.5bb | 5.5bb | 17.7 |
| CO vs. BTN 3-bet pot | 92.5bb | 16.5bb | 5.6 |
| CO vs. BTN 4-bet pot | 79bb | 43.5bb | 1.8 |
How SPR affects our decision-making
When SPR is high, we have committed relatively few chips compared to our stack. There is more room for future betting, so our strongest hands become especially important. If we want to play for stacks with a nutted hand, we usually need to start building the pot early or use larger bet sizes on later streets.
At high SPRs, medium-strength hands need more caution. A hand like top pair becomes less comfortable when playing for stacks when only a small portion of the stack is currently committed to the pot. This is because opponents don't lose much when they fold in a small pot, but they can win a lot when they get stacks in with the nuts.
Being out of position also becomes harder as SPR increases. The OOP player has to act first on future streets, which makes it harder to control the pot size and realize equity. For that reason, OOP players often prefer lower SPRs, where decisions are simpler and strong one-pair hands can realize value more directly.
When SPR is low, less betting is required to get all-in. Smaller bets can still commit a large share of the remaining stack, and hands like top pair, overpairs, and strong ace-high holdings can become natural stack-off candidates.
At low SPRs, medium-strength hands are more comfortable stacking off. This is one reason strong hands like overpairs and AK often want to 3-bet or 4-bet preflop. By putting more money into the pot before the flop, they reduce the postflop SPR and give these hands good spots to get stacks in with hands like top pair or overpairs.
Preflop dynamics
Effective stack depth changes which preflop hands perform well.
At low effective stacks, such as 20bb, high-card strength becomes more important. Hands like AJo, KQo, and medium pairs can make strong pairs or overpairs and are often comfortable committing because we are less worried about our opponents stacking us with nutted hands.
At medium effective stacks, such as 100bb, speculative hands gain value. Suited connectors, suited broadways, suited aces, and small pairs can win larger pots when they make strong disguised hands like sets or straights.
At deep effective stacks, such as 200bb or more, nut potential becomes even more important. Suited aces can make nut flushes, connected hands can make nut straights, and small pairs can win large pots when they flop sets. The deeper the stacks, the more dangerous it becomes to build huge pots with non-nutted one-pair hands.
Common stack-depth mistakes
Beginners often:
- overvalue hands at high SPRs and undervalue hands at low SPRs.
- are scared to overbet (bet larger than the pot) at high SPRs and miss opportunities to get stacks in with nutted hands.
- bet too large at low SPRs.
- trap with strong hands preflop and end up playing for small pots with premium hands like AA.
Key takeaways
- High SPRs reward nutted hands, careful pot control with medium-strength hands, and planning across multiple streets.
- Low SPRs lower the threshold for stacking off because nuts are less of a consideration.
- Preflop action shapes postflop SPR. Raises, 3-bets, and 4-bets manipulate the SPR and affect how the rest of the hand will play.
- Good players think about both the current SPR and how actions will affect the SPR on future streets.