Roulette probability is straightforward to calculate. On a European wheel, the probability of any single number winning is 1 in 37 (2.7%). For red or black bets, the probability is 18 in 37 (48.6%) due to the zero. Inside bets covering multiple numbers have higher probabilities but lower payouts, while outside bets offer better odds but smaller returns. The mathematical relationship between probability and payout odds determines expected value over many spins.
A straight bet on one number pays 35:1, while the true odds are 36:1, creating the house advantage. Understanding this distinction between payout odds and true probability is essential for informed gambling decisions. Consistent application of mathematical principles helps players recognize which bets offer relatively better value.