A standard European roulette wheel contains 37 numbers (0-36), while American roulette features 38 numbers (0, 00, and 1-36). Understanding wheel mechanics is fundamental to grasping probability calculations. Each number has an equal probability of occurring on any given spin, assuming the wheel is fair and properly maintained.
The presence of zero (and double zero in American roulette) gives the house its mathematical advantage. This single number represents the house edge—the reason casinos maintain long-term profitability. In European roulette, the house edge is 2.7% (1 divided by 37). In American roulette, the house edge increases to 5.26% due to the additional double-zero pocket.
Wheel bias and mechanical wear are theoretical concerns that some players discuss, but modern casino standards ensure wheels are regularly maintained, tested, and rotated to prevent exploitation. Understanding that roulette outcomes are independent events—meaning previous results don't influence future spins—is crucial for realistic expectations.
Inside and Outside Bets
Roulette offers two primary betting categories. Inside bets include straight bets (single numbers), splits (two numbers), streets (three numbers), corners (four numbers), and lines (six numbers). These carry higher payouts but lower probability of winning. Outside bets encompass red/black, odd/even, high/low, columns, and dozens. These offer lower payouts but higher probability of success, typically around 48.6% in European roulette.