Geometric Bet Sizing to Get Stacks In by the River

Geometric bet sizing means betting the same fraction of the pot on every remaining street, chosen so the last bet is exactly all-in. With an SPR of 4 and three streets to play, that fraction is about 54% of the pot: $54, then $112, then $234 into a starting pot of $100. One piece of arithmetic turns "how do I get stacks in?" into a question you answer before the flop bet, not after you have sized yourself into an awkward river.

What geometric sizing actually means

Most players size each street on instinct and discover on the river that the plan does not close. A third of the pot on the flop, half on the turn, and they arrive with 90% of the stack behind and a pot too small to justify it. The last bet is either a wild overbet or a whimper.

Geometric sizing removes that. You pick how many streets you intend to bet, work backwards from the stack, and every bet is the same fraction of the pot at the time.

Because the pot grows each time both players put money in, equal fractions produce sharply growing amounts. That is the whole trick: constant pressure in percentage terms, escalating pressure in chips.

Everything starts with the stack to pot ratio at the moment you decide to bet. Nothing else about the hand changes the number.

The formula

Each time you bet a fraction f of the pot and get called, the pot multiplies by (1 + 2f). Do that n times and both stacks are in the middle.

Bet size as a fraction of pot = ((1 + 2 × SPR)^(1/n) − 1) ÷ 2, where n is the number of streets you still intend to bet.

Run it at an SPR of 4 over three streets. Twice the SPR is 8, plus one is 9. The cube root of 9 is about 2.08; subtract one, halve it, and you get 0.54 — a 54% pot bet on flop, turn and river.

You never actually compute this at the table. Only a handful of SPRs come up regularly, so you learn the answers once and recognise them on sight.

The sizes worth knowing by heart

The table gives the geometric fraction for the SPRs you will actually face. If you are betting one street only, the answer is trivial: your bet is SPR times the pot.

SPR	Three streets	Two streets
1	22%	37%
2	36%	62%
3	46%	82%
4	54%	100%
6	68%	130%
8	79%	156%
13	100%	210%

Notice how fast the sizes climb past an SPR of 6. That is the honest signal that a three-street plan is getting expensive, and often the point where checking a street beats jamming the accelerator.

A hand from flop to river

You raise the CO with A♠K♠, the BB calls, and the flop comes K♦8♠3♣. The pot is $100 and you both have $400 behind — an SPR of 4. Top pair top kicker on a dry board, and you want the stack in.

• Flop: bet $54 into $100. Called. Pot is $208, you have $346 left.
• Turn: bet $112 into $208. Called. Pot is $432, you have $234 left.
• River: bet $234 into $432. That is your last chip, and it is 54% of the pot.

No street is uncomfortable. No bet is so large that only better hands continue, and no bet is so small that you strand chips.

Compare the common alternative: $35, then $80, then a $285 shove into a $330 pot. The first two bets pressure nothing and the river folds out most of what you beat.

The plan only works if you beat what calls all three streets. A poker equity calculator settles that in seconds, and top pair against a set-and-two-pair calling range is a very different hand from top pair against second pair.

Why equal fractions win

The argument is short. A defender facing a bet has to continue with pot ÷ (pot + bet) of their range to stop you profiting with any two cards, so bigger bets let them fold more.

Bet three streets and the chance they are still there at the end is the product of three continuing frequencies. You want to maximise that product while still getting the full stack in.

The arithmetic resolves the way it does for any product with a fixed total: keep the terms equal. One huge street followed by two small ones sheds more range than three even bets do, and you finish all-in against fewer hands.

The differences are not enormous, which is the practical point. Being roughly geometric captures nearly all of the value, so size to a plan rather than agonising over three percentage points.

When geometric sizing is the wrong plan

Geometric sizing answers one question: how do I get the stack in over n streets? If that is not the question, the formula does not apply.

• You are not betting three streets. On a board that hits the caller's range hard, a checked street is the plan, not a failure of it.
• You are value betting thin. Second pair is not trying to get $400 in. This is a tool for polarised, nutted value.
• Protection dominates. With two flush draws and an open-ender out there, a larger flop bet that charges draws can beat the flat line.
• The SPR is very deep. At an SPR of 8 the line asks for 79% pot three times running, which prices in far too much of their range.
• You are multiway. Two callers defend more total range than one, and the tidy two-player arithmetic stops describing the pot.

The river is also where the plan gets abandoned on purpose. When the last card leaves your range polarised and theirs capped, overbetting the river extracts more than the geometric size, and the elegance of the line is worth nothing on its own.

Using it at the table

1. Count the SPR when the flop lands. Effective stack divided by pot, before anything else.
2. Decide how many streets you want. Three on a dry board with a strong hand, two if you expect to check somewhere, one if you are nearly all-in already.
3. Read the size off the table. SPR 4 over three streets is 54%. SPR 2 is 36%. Round to something ordinary and bet it.
4. Recompute on the turn. If a raise, a scare card or a decision to give up a street changed the plan, redo it with the streets you have left.

That last step matters most. Geometric sizing survives contact with only some hands, and the wider question of bet sizing strategy on each street never reduces to one formula.

What it gives you is a default worth deviating from: you know what the river bet will be while you are still choosing the flop one. Players who size this way stop leaving money behind on rivers and stop shoving stacks that were never getting called — two quiet, expensive leaks fixed by one number counted at the start of the hand.