An out is a card that turns a losing hand into a winning one. Counting them is the input to every drawing decision; converting them to a percentage is mechanical.
The shortcut, and its limits
The rule of 2 and 4 is the standard mental method: multiply your outs by 2 for one card to come, or by 4 for two cards. It is fast and it is approximately right, which is all a table shortcut needs to be.
It is not exactly right, and the error is not symmetric. Multiplying by 4 treats the turn and river as two independent 2%-per-out chances and forgets that hitting on the turn makes hitting on the river redundant, so it double-counts. That double-count grows with the number of outs.
| Outs | One card to come | Two cards to come | Rule of 4 |
|---|---|---|---|
| 4 | 8.5% | 16.5% | 16% |
| 5 | 10.6% | 20.4% | 20% |
| 6 | 12.8% | 24.1% | 24% |
| 7 | 14.9% | 27.8% | 28% |
| 8 | 17.0% | 31.5% | 32% |
| 9 | 19.1% | 35.0% | 36% |
| 10 | 21.3% | 38.4% | 40% |
| 11 | 23.4% | 41.7% | 44% |
| 12 | 25.5% | 45.0% | 48% |
| 13 | 27.7% | 48.1% | 52% |
| 14 | 29.8% | 51.2% | 56% |
| 15 | 31.9% | 54.1% | 60% |
Below about eight outs the rule of 4 is accurate to within a point and you can use it without thinking. Above that it drifts, and by fifteen outs it claims 60% when the truth is 54.1% — nearly six points of pure optimism, applied to precisely the monster draws where people are most inclined to get their stack in.
The field fix is to subtract the excess above eight: for n outs over eight, use 4n − (n − 8). At fifteen outs that gives 53%, against a true 54.1%. Close enough.
The bigger flaw nobody mentions
The arithmetic error is minor next to a structural one. The rule of 4 prices two cards, but you rarely get two cards for one bet.
If you call a flop bet, you see the turn. You do not automatically see the river — your opponent usually bets again, and you have to pay again. So comparing a 35% two-card equity against the odds you are being offered on the flop quietly assumes a free river card that is not on offer.
Use the two-card number when you or your opponent are all in on the flop, or when you are confident the turn will check through. In every other case, price the flop call against the one-card figure and reassess after the turn. A flush draw facing a half-pot flop bet needs 25%, and it has 19.1% to the turn, not 35%. That gap is where implied odds have to do their work, and where a lot of losing money lives.
Discount your outs
Raw out counts assume every card that makes your hand also wins the pot. Often it does not.
- The card that makes your hand makes theirs. A four-flush board completing when you hold the second-best flush is an out that costs you your stack.
- Board-pairing outs. Making your straight on a card that pairs the board hands a full house to anyone holding two pair or a set.
- Overcards that are not clean. Holding two overcards to the board is six outs to a pair — but if your opponent has a set, all six are worthless, and against a better kicker the ace you pair may still lose.
The practical adjustment is to count full outs, half outs and zero outs rather than pretending precision. A nine-out flush draw against a range containing sets is realistically closer to eight. That is not a rounding error in a close spot.
Standard draws at a glance
| Draw | Outs | Turn | By the river |
|---|---|---|---|
| Gutshot straight draw | 4 | 8.5% | 16.5% |
| Two overcards, to a pair | 6 | 12.8% | 24.1% |
| Open-ended straight draw | 8 | 17.0% | 31.5% |
| Flush draw | 9 | 19.1% | 35.0% |
| Flush draw plus gutshot | 12 | 25.5% | 45.0% |
| Flush draw plus open-ender | 15 | 31.9% | 54.1% |
Before the flop
A handful of preflop numbers come up often enough to be worth knowing outright. There are 1,326 possible two-card combinations, which reduce to 169 distinct starting hands once suits are grouped.
| Event | Chance |
|---|---|
| Dealt one specific pocket pair (aces, say) | 0.45% — about 1 in 221 |
| Dealt any pocket pair | 5.9% — 1 in 17 |
| Dealt two suited cards | 23.5% — about 1 in 4 |
| Dealt one specific suited hand | 0.30% — about 1 in 332 |
| Dealt ace-king in any form | 1.2% — about 1 in 83 |
| A pocket pair flopping a set or better | 11.8% — about 1 in 8.5 |
| Two suited cards flopping a flush draw | 10.9% |
| Two unpaired cards flopping at least a pair | 32.4% |
The last two explain a lot of losing play. Suited cards flop a flush draw about one time in nine, and complete it far less often than that, so the suit is a small bonus rather than a reason to play a hand. And two unpaired cards miss the flop entirely about two thirds of the time — which is also true of your opponent, and is the entire reason continuation betting works.
Once you have the equity number, take it to the pot odds calculator and compare. If you are playing a tournament, remember that chips are not money and the break-even point moves against you.