Stack-to-pot ratio
Stack-to-pot ratio (SPR) is one number that says how committed the money already is: the effective stack still behind, divided by the pot, measured when the flop arrives. Preflop already chose it — every raise you make or call is also a decision about the geometry of the streets to come.
Three pots, three geometries (100bb, small blind's 0.5bb dead)
Each row computes the flop pot, the stack behind, the SPR, and the geometric bet — the equal pot-fraction that gets the stacks in over exactly three streets.
| Pot type | Preflop | Flop pot | Behind | SPR | Geometric bet |
|---|---|---|---|---|---|
| Single-raised | BTN opens 2.5bb, BB calls | 5.5bb | 97.5bb | 17.7 | 116% pot |
| 3-bet | BTN 2.5bb, BB 3-bets to 11bb, BTN calls | 22.5bb | 89bb | 4.0 | 54% pot |
| 4-bet | BTN 2.5bb, BB to 11bb, BTN 4-bets to 24bb, BB calls | 48.5bb | 76bb | 1.6 | 30% pot |
Low SPR simplifies. In the 3-bet pot, three ordinary half-pot bets put the stacks in — so a hand like an overpair can typically commit without ever making an oversized bet, and there's little room to maneuver away from it. In the 4-bet pot the flop is nearly a formality. High SPR demands judgment: in the single-raised pot, stacks only go in via repeated overbets, which means anyone building that pot is typically announcing a range that beats one pair. The same top pair is a commit at SPR 1.6 and a pot-controlled hand at SPR 17.7.
This cuts both ways before the flop. Raising bigger — or 3-betting — with hands that flop strong-but-one-pair (big aces, big pairs) buys the low SPR they want; flatting with implied-odds hands (suited connectors, small pairs) keeps the SPR high so the rare monster gets paid across three full streets. Topic 7's range logic and this lesson's geometry are two views of the same preflop decision.
This app grades each street's bet against the live ranges and pot — SPR is the planning lens you bring to the table, not an input the grader scores directly. Where it shows up in your grades is indirect and real: the low-SPR stack-off that's fine in a 3-bet pot prices out as a blunder in the single-raised one, because the ranges and ratios differ exactly the way this table says.