Roulette
A casino wheel game where players bet on which numbered pocket a spinning ball will land in.
Definition
Roulette is a table game played on a spinning wheel divided into numbered pockets, plus one or two green zero pockets, with a betting layout where players stake on a single number, a group of numbers, or an even-money property such as red/black or odd/even. A ball is spun against the wheel's rotation and settles into one pocket, deciding all bets for that spin. The house edge comes from the zero pockets: winning payouts are calculated as if the zeros did not exist, so single-zero (European) wheels carry a lower edge than double-zero (American) wheels. Because every spin is statistically independent, no betting pattern changes the underlying odds over time.
Worked example
A single-number ("straight up") bet on European Roulette pays 35 to 1, but there are 37 pockets (0-36), so the true odds of winning are 36 to 1. A player staking 1 unit on one number has a 1/37 chance to win 35 units and a 36/37 chance to lose 1 unit, giving an expected value of (1/37 x 35) + (36/37 x -1) = -1/37 ≈ -0.027 per unit. That is the standard 2.70% house edge on European Roulette; the American wheel adds a second zero (00) for 38 pockets, raising the edge on the same bet to 2/38 ≈ 5.26%.
Why it matters
Roulette is one of the clearest teaching examples of house edge, because the gap between the "35 to 1" payout and the "36 to 1" true odds makes the operator's mathematical advantage visible in a single calculation. Understanding it helps learners see why table variant matters (single-zero vs double-zero, and rules like La Partage that halve the edge on even-money bets), how independence of spins undercuts "system" betting, and how RTP is derived and communicated to players. For professionals, it underpins accurate game-fairness disclosures, responsible-gambling messaging, and margin modelling.
Related
Note: The 2.70% (European) and 5.26% (American) house-edge figures and the 35:1 straight-up payout are stable, standard values. However, the edge on even-money bets varies by rule set: French Roulette's La Partage or En Prison rules roughly halve it to about 1.35% on those bets, and some tables use triple-zero wheels with a higher edge. Payout tables, available variants, and permitted rules differ by operator and jurisdiction and should be verified against the specific game's paytable.