Roulette Probability and Odds Explained
Roulette probability is the chance of any bet winning on a single spin. Odds are the payout the casino offers when that bet wins. The gap between the two is the house edge, which is 2.70% on European roulette and 5.26% on American roulette.
What Is Roulette Probability?
Probability is the proportion of pockets a bet covers, divided by the total number of pockets on the wheel. On European roulette there are 37 pockets (0-36). On American roulette there are 38 (0, 00, 1-36).
A straight-up bet covers one pocket, so its probability is 1/37 on European (about 2.70%) and 1/38 on American (about 2.63%). A red/black bet covers 18 pockets, so its probability is 18/37 on European (about 48.65%).
Payout Odds Explained
Payouts are quoted as ratios. A 35:1 payout means a winning one-unit bet returns 35 units of profit (plus the original stake). A 1:1 payout returns one unit of profit. The casino sets payouts so that even when you win, the long-term expectation tilts in its favour.
Probability and Payouts by Bet
| Bet | Coverage | Payout | European probability | American probability |
|---|---|---|---|---|
| Straight-up | 1 number | 35:1 | 2.70% | 2.63% |
| Split | 2 numbers | 17:1 | 5.41% | 5.26% |
| Street | 3 numbers | 11:1 | 8.11% | 7.89% |
| Corner | 4 numbers | 8:1 | 10.81% | 10.53% |
| Six-line | 6 numbers | 5:1 | 16.22% | 15.79% |
| Column / Dozen | 12 numbers | 2:1 | 32.43% | 31.58% |
| Even-money | 18 numbers | 1:1 | 48.65% | 47.37% |
What Is the House Edge?
The house edge is the long-term percentage of every wagered unit the casino keeps. It comes from the gap between the true odds of an event and the payout offered. For example, a straight-up bet's true odds on European roulette are 36 to 1, but the payout is 35 to 1. That missing one unit per 37 spins is the 2.70% edge.
Probability vs Short-Term Variance
Probability describes long-term behaviour. Short-term results can swing in either direction. A 48.65% even-money bet can lose ten in a row, and a 2.70% straight-up bet can hit twice in five spins. Neither outcome is suspicious - both fit inside expected variance.
Practical Use of Probability
Treat probability as a budgeting tool, not a prediction tool. If you bet 100 units on red on European roulette, expected loss per spin is 2.70 units. Over 100 spins, that compounds to about 270 units in expected loss - before counting variance.
Test these numbers against your own session on the free roulette demo for hands-on intuition.
For more on roulette mechanics, variants, and odds, return to the main roulette guide. To put these ideas into practice, the free roulette demo on the homepage is built for risk-free experimentation with every bet type and variant covered here.