Roulette Probability Calculator
Calculate exact odds and expected value for every roulette bet type.
Compare American (38 slots) vs European (37 slots) wheel probabilities.
Roulette Wheel Layout The European roulette wheel (invented in France in the 1790s) has 37 slots: numbers 1-36 alternating red and black, plus one green 0. The American roulette wheel adds a second green slot (00), making 38 total. This extra slot nearly doubles the house edge.
How Probability Works in Roulette Probability = (favorable outcomes) / (total outcomes). For a straight-up bet on a single number on a European wheel: P = 1/37 = 2.70%. On an American wheel: P = 1/38 = 2.63%. The payout is 35:1 for both wheels, but the true odds differ.
House Edge The house edge is the difference between the true odds and the payout odds. European wheel: (37-36)/37 = 2.70% house edge. American wheel: (38-36)/38 = 5.26% house edge. This means for every $100 bet over time, you can expect to lose $2.70 (European) or $5.26 (American).
Common Bet Types Straight Up: 1 number, pays 35:1. Split: 2 numbers, pays 17:1. Street: 3 numbers, pays 11:1. Corner: 4 numbers, pays 8:1. Six Line: 6 numbers, pays 5:1. Dozen/Column: 12 numbers, pays 2:1. Red/Black, Odd/Even, High/Low: 18 numbers, pays 1:1.
The Gambler’s Fallacy Each spin is independent. If red has come up 10 times in a row, the probability of red on the next spin is still exactly the same. The wheel has no memory. Casinos encourage this fallacy by displaying previous results on electronic boards.
La Partage and En Prison Rules Some European casinos use “La Partage” — if the ball lands on 0 and you placed an even-money bet, you get half your bet back. This reduces the house edge to just 1.35%, making it one of the best bets in any casino.