Split
One chip across the line between two adjacent numbers.
Two numbers out of 37, pays 17:1. ProbabilitymathProbabilityChance of an outcome, from 0 to 1 or 0% to 100%. One number: 1/37 = 2.70%.Read full → 5.41%, house edgemathHouse edgeThe share of each stake the casino keeps on average: 2.70% in European roulette.Read full → 2.70%.
Placement
The chipmoneyChipA token representing a fixed amount, placed on the layout to make a bet. Also: check.Read full → straddles the shared edge of two cells. Horizontal splitsbetSplitTwo adjacent numbers, pays 17:1.Read full → pair numbers in the same row (17-18); vertical splits pair numbers in the same columnbetColumnTwelve numbers in one vertical column of the layout, pays 2:1.Read full → (17-20). ZerowheelZeroThe single green pocket that no even-money, dozen or column bet covers; the source of the house edge. Also: single zero, 0.Read full → splits with 1, 2 or 3 along its lower edge. On a 3×12 grid there are 57 ordinary splits plus the three with zero, 60 in all. A chip that touches a cornerbetCornerFour numbers sharing a corner on the layout, pays 8:1.Read full → rather than an edge is a corner bet, so place it centered on the line.
Payout and expectation
Fair odds against two numbers in 37 are 17.5 to 1; the table pays 17. On a $10 chip a hit returns $170 of winnings and the stake. Over 37 average spins you win twice (+$340) and lose 35 times (−$350), net −$10 on $370 wagered: 2.70%.
Character
Half the variancemathVarianceA measure of how widely results spread around the expected value. High for straight up, low for even-money bets.Read full → of a straight upbetStraight upA single number, pays 35:1.Read full → for the same expected lossmathExpected lossExpected value times total amount wagered; the average amount lost over a session or a period.Read full →. The split is the natural compromise for players who want the inside-bet feel without 36 losing spins between hits. It is also the building block of the tiers du cylindreFR · sectorTiers du cylindre“Third of the wheel”: the twelve numbers opposite zero, 27 to 33 on the wheel, bet with six splits.Read full → call bettableCall betA bet announced to the dealer rather than placed by hand, usually a wheel-sector bet such as voisins or tiers. Also “announced bet”.Read full →, which is six splits covering twelve pocketsequipmentPocketOne of the 37 numbered compartments on the rotor. Also: slot, cup.Read full → on one third of the wheel.
On the wheel
LayoutequipmentLayoutThe printed betting grid on the table. Also: table, felt, cloth.Read full → neighborsbetNeighborsA number and the two pockets on either side of it on the wheel, five straight-up chips.Read full → are not wheel neighbors. 17-18 sits on opposite sides of the wheel (17 is between 25 and 34; 18 is between 22 and 29). No split covers two pockets that touch on the wheel; the nearest is 0-3, two pockets apart with 26 between them. The American wheel has one exception: 0 sits between 28 and 2, and 0-2 is a split on the American layout. In practice a split is purely a layout bet.
French usage
À chevalFR · splitChevalFrench for split: one chip on the line between two numbers, pays 17:1.Read full →, “on horseback”: the chip sits astride the line like a rider. French dealers accept the call “cheval douze-quinze” and place it for you. On the racetracktableRacetrackThe oval strip on live and electronic layouts showing the numbers in wheel order, used to place neighbors and sector bets in one tap.Read full →, the tiers button places six chevaux at once.
Questions
Only on an American layout, where it pays 17 to 1 and carries the 5.26% edge like everything else there.
A $10 split and two $5 straight ups on the same numbers are the same bet: same cover, same payoutmoneyPayoutWhat a winning bet returns, quoted as “X to 1” on top of the returned stake.Read full →, same variance.
√(p·17² + (1−p) − EV²) with p = 2/37. See the variance page.
Fun with Math
Try these yourself first. Each solution is folded; open it when you are ready.
On which wheel, European or American, does any splitbetSplitTwo adjacent numbers, pays 17:1.Read full → cover two pocketsequipmentPocketOne of the 37 numbered compartments on the rotor. Also: slot, cup.Read full → that sit side by side on the wheel?
Show the solution
Answer Only on the American wheel, and only one: 0-2.
On the European wheel zerowheelZeroThe single green pocket that no even-money, dozen or column bet covers; the source of the house edge. Also: single zero, 0.Read full → sits between 32 and 26, and its splits on the layoutequipmentLayoutThe printed betting grid on the table. Also: table, felt, cloth.Read full → are 0-1, 0-2 and 0-3. None of the other 57 splits pairs two wheel neighborsbetNeighborsA number and the two pockets on either side of it on the wheel, five straight-up chips.Read full → either: the wheel order was designed to scatter numbers that sit close together on the layout.
On the American wheel zero sits between 28 and 2, and 0-2 is a split on the American layout. Double zerovariantDouble zeroThe 00 pocket of the American wheel. Its presence raises the house edge from 2.70% to 5.26%.Read full → sits between 1 and 27, but its splits are 00-2, 00-3 and 0-00.
Comic relief
Centered on the line. The dealer’s reading is final.
Sources
- Ethier, S. N. The Doctrine of Chances: Probabilistic Aspects of Gambling.