Off the FeltPoker math
The rule of 2 and 4 in poker, and where it lies
Multiply your outs by 2 for one card to come. Multiply by 4 for two. It is the fastest way to turn outs into a percentage, and it is wrong in two places worth knowing.
The rule
You have a flush draw on the flop: 9 outs.
- One card to come: 9 × 2 = about 18%. The exact number is 19.1%.
- Two cards to come: 9 × 4 = about 36%. The exact number is 35.0%.
Close enough to act on. That is the point of it.
Where it lies, one: you rarely see two cards
The rule of 4 assumes you see the turn and the river. You usually do not. He bets the flop, you call, and he bets the turn too. If you are calling one bet and expect another, you are buying one card, not two. Use the rule of 2.
This is the most expensive misuse of the rule. Use 4 only when someone is all in on the flop, or when you are sure there will be no turn bet.
Where it lies, two: big draws
With more than 8 outs, the rule of 4 runs high. The fix is easy: multiply by 4, then subtract the outs above 8.
- 15 outs: 60 minus 7 = 53%. Exact: 54.1%.
- 12 outs: 48 minus 4 = 44%. Exact: 45.0%.
The rule against the exact odds
From the flop, with 47 unseen cards.
| Draw (outs) | ×2 | One card | ×4, fixed | Two cards |
|---|---|---|---|---|
| Gutshot (4) | 8% | 8.5% | 16% | 16.5% |
| Two overcards (6) | 12% | 12.8% | 24% | 24.1% |
| Open-ender (8) | 16% | 17.0% | 32% | 31.5% |
| Flush draw (9) | 18% | 19.1% | 35% | 35.0% |
| Flush draw and gutshot (12) | 24% | 25.5% | 44% | 45.0% |
| Flush draw and open-ender (15) | 30% | 31.9% | 53% | 54.1% |
"×4, fixed" subtracts the outs above 8. Below 9 outs it is the plain rule of 4.
Putting it to work
The rule gives you your chance to hit. Hold it against the price from pot odds. Pot 100, he bets 50: the price is 25%. A flush draw with one card to come is about 18%. Fold, unless there is money behind that he will pay you when you hit. If he is all in, it is about 36% against 25%. Call.
Against a made hand, the exact answer is your equity. The rule is how you get near it in the seconds you have.
Off the Felt makes you do this arithmetic on the clock, so the right number shows up at the table.
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