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Flawless Poker

Universal Law 03

ORBITAL MECHANICS

Outs, turn, and river

Count the unseen cards that complete the hand, then read how often they arrive. The shortcut is close. It is not the law.

After the flop, 47 cards are unseen. On the turn, 46 remain. Turn in the table is the chance the next card is an out. River is the chance from the turn, one card left. Turn and river together is the chance of hitting on either card when you are all in on the flop.

One card is outs ÷ 47, or outs ÷ 46 from the turn. Two cards is one minus the chance of missing both:

1 − ((47 − outs) ÷ 47) × ((46 − outs) ÷ 46)

Chance a stated number of clean outs arrives. The rule of 4 is outs × 4. The error is that shortcut minus the true two-card chance.
OutsTurnRiverTurn + riverRule of 4Error
12.1%2.2%4.3%4%−0.3
24.3%4.3%8.4%8%−0.4
36.4%6.5%12.5%12%−0.5
48.5%8.7%16.5%16%−0.5
510.6%10.9%20.4%20%−0.4
612.8%13.0%24.1%24%−0.1
714.9%15.2%27.8%28%+0.2
817.0%17.4%31.5%32%+0.5
919.1%19.6%35.0%36%+1.0
1021.3%21.7%38.4%40%+1.6
1123.4%23.9%41.7%44%+2.3
1225.5%26.1%45.0%48%+3.0
1327.7%28.3%48.1%52%+3.9
1429.8%30.4%51.2%56%+4.8
1531.9%32.6%54.1%60%+5.9
1634.0%34.8%57.0%64%+7.0
1736.2%37.0%59.8%68%+8.2
1838.3%39.1%62.4%72%+9.6
1940.4%41.3%65.0%76%+11.0
2042.6%43.5%67.5%80%+12.5

Multiply outs by 2 for one card and by 4 for two. The ×2 version stays close on every row, a little low. The ×4 version is useful through about 8 outs, then it overshoots: 3 points at 12 outs, 5.9 at 15, and 12.5 at 20, where it claims 80% and the count is 67.5%. A common patch above 8 outs is ×4, then subtract (outs − 8). For 15 outs that patch says 53, against a true 54.1%.

FLAWLESS POKER / STUDY CHART

Outs to equity: exact chance versus quick rules

Line chart for one to fifteen clean outs. Four outs hit by the river about 16.5 percent of the time; eight outs about 31.5 percent; nine outs about 35 percent. It compares exact hit chances with the rule of two and four estimates.
The solid lines show the chance to hit at least one of a specified number of clean outs from flop to river or turn to river. The dashed rules of 4 and 2 are quick estimates that diverge as outs increase. Hitting an out is not the same as winning the pot, and an out may be blocked or make an opponent stronger. Open full-size chart ↗

These counts are for study and post-session review. Where a row comes from a simulation, the caption names how many deals were run. Where a stack or a pot is made up, the caption says so. None of these figures is an instruction for a live pot.