How outs become equity
After the flop, 47 cards are unseen. With N outs your chance of missing both the turn and the river is (47−N)/47 × (46−N)/46, and your equity is one minus that.
With one card to come it is simply N/46.
Every common draw
| Draw | Outs | Flop to river | Rule of 4 | Error | Turn to river |
|---|---|---|---|---|---|
| Flush draw | 9 | 34.97% | 36% | +1.03 | 19.57% |
| Open-ended straight draw | 8 | 31.45% | 32% | +0.55 | 17.39% |
| Gutshot straight draw | 4 | 16.47% | 16% | -0.47 | 8.70% |
| Two overcards | 6 | 24.14% | 24% | -0.14 | 13.04% |
| Flush draw plus gutshot | 12 | 44.96% | 48% | +3.04 | 26.09% |
| Flush draw plus open-ender | 15 | 54.12% | 60% | +5.88 | 32.61% |
| Set to full house or quads | 7, then 10 | 33.40% | 28% | -5.40 | 21.74% |
| Pocket pair to a set | 2 | 8.42% | 8% | -0.42 | 4.35% |
Where the shortcut breaks
The rule of 4 and 2 says: multiply your outs by four with two cards to come, by two with one. It is a good rule, and when your outs are the same on both cards it fails in a predictable direction.
On small draws it is accurate to within half a point, and it actually understates a gutshot slightly. On large draws it overstates badly: a flush draw with an open-ended straight draw has 15 outs and real equity of 54.12%, while the rule says 60%. That is 5.88 percentage points of optimism at exactly the moment you are committing the most chips.
The reason is double counting. Multiplying by four assumes the turn and river are independent chances, but if the turn hits your draw the river is irrelevant. The more outs you have, the more often that happens, and the more the rule overcounts.
One row breaks the other way, and it is the case the rule cannot see. A flopped set has 7 outs on the turn and 10 on the river, because every blank turn card adds three more cards that pair it, so the rule's 28% understates the set's 33.40% by 5.40 points.
The correction worth remembering
Above about eight outs, subtract roughly one point for every out over eight. On a 15-out draw that turns 60% into about 53%, which is close to the real 54.12%.
Or simply remember two anchors: a flush draw is 35% and an open-ender is 31% from flop to river. Those two cover most of the decisions you will actually face.
Turning equity into a call or a fold is the job of our pot odds page.
Frequently Asked Questions
- How accurate is the rule of 4 and 2?
- Within half a percentage point up to about eight outs, when the outs are the same on both cards. On a 15-out draw it overstates your equity by 5.88 points; on a flopped set, whose outs grow from 7 to 10 on the river, it understates it by 5.40.
- What is the equity of a flush draw?
- 34.97% from flop to river, and 19.57% with only the river to come.
- Why does the rule overstate big draws?
- It treats the turn and river as independent chances. If the turn completes your draw the river no longer matters, and the more outs you hold the more often that happens.
- What is the exact formula?
- 1 − (47−N)/47 × (46−N)/46 with two cards to come, and N/46 with one.
Corrected on 18 October 2026: a flopped set has 7 outs on the turn and 10 on the river, so from the flop it improves 33.40% of the time (1 - 40/47 x 36/46), not 38.39%; the 21.74% with one card to come is from the turn.
Corrected on 19 October 2026: the set row added on 18 October contradicted this page's summary that the rule is within half a point up to eight outs and fails in a predictable direction (under on small draws, over on large ones). That holds when the outs are the same on both cards; the set, whose outs grow, is now named as the exception.
Equities on this page are computed by enumerating every one of the 1,712,304 boards that can follow the two hands shown, not by simulation, so they are exact for those specific cards. Draw and flop probabilities are exact combinatorics. The hand evaluator is checked against known orderings and the equities against published ranges before publication. Note that published figures usually quote one number per hand class while the real value moves with the suits, which is why this section names the exact cards.