Roulette is one of the most recognisable games found in any casino, whether you are playing online or visiting a venue in person. With its spinning wheel, colourful layout, and simple rules, it draws plenty of interest.
If you have wondered how casinos still make money from a game that pays out regularly, the answer sits in the maths behind the wheel.
This article explains where the edge comes from, how it affects every bet, and what that means each time the ball lands. Read on to learn more.
What Is Roulette and How Does It Work?
Roulette is found in both physical casinos and online. The game centres on a spinning wheel with numbered pockets and a felt betting layout. The most common version in the UK is European roulette, which has 37 pockets numbered 0 to 36.
Players place chips on the layout to predict where the ball will land. Bets can be on a single number, a combination of numbers, a colour, or whether the result will be odd or even. Each bet has a stated payout, shown on or near the table.
Once bets are placed, the dealer spins the wheel in one direction and the ball in the other. When the ball settles in a pocket, winning bets are paid according to the displayed odds and losing bets are collected.
Online versions use the same rules. In digital games, outcomes are produced by a Random Number Generator (RNG), while live dealer tables stream a real wheel with a human croupier. Tables can differ slightly in layout or rules, so it could help to glance at the information panel before you potentially start.
Players should always remember to gamble responsibly and within their means- never wager more than you can afford to lose.
Understanding the House Edge in Roulette
The house edge is the built-in advantage a casino has on every bet. In roulette, it comes from the difference between the true probability of an outcome and the payout you receive when that outcome occurs.
On a European wheel there are 37 possible results, yet a straight-up bet on one number pays 35 to 1. If payouts matched the true chance of 1 in 37, the return would be 36 to 1. Paying 35 to 1 instead of 36 to 1 leaves a margin in the casino’s favour. Averaged over time, that margin is 2.7% on European roulette, which means about £2.70 kept by the house for every £100 wagered across many spins.
French roulette sometimes reduces this edge on even-money bets through rules such as La Partage or En Prison, returning or holding half the stake when zero appears. With those rules, the effective edge on even-money wagers can drop to 1.35%.
Some online games add side bets or tweak payouts. These changes can increase or decrease the edge, so it could be worth checking the paytable and rules to see how that particular table is set up.
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Why Do Single Zero and Double Zero Wheels Have Different Odds?
European roulette uses a single zero wheel with 37 pockets. American roulette adds a double zero, creating 38 pockets. That extra pocket slightly lowers the chance of any specific outcome without changing the listed payouts.
For example, a straight-up bet has a 1 in 37 chance on a European wheel but a 1 in 38 chance on an American wheel, while both still pay 35 to 1. Even-money bets, such as red or black, are also affected. On European tables, 18 of the 37 pockets are red, 18 are black and one is zero. On American tables there are 18 red, 18 black and two greens, zero and double zero. The more non-red and non-black pockets there are, the fewer spins those even-money bets will win over time.
This shift increases the casino’s edge on American roulette to about 5.26%. In the UK, single zero wheels are the norm in both physical and online settings, though some online platforms do offer both types. Knowing which wheel you are playing might help you understand the underlying probabilities.
How Much Advantage Does the Casino Have on Each Bet?
On European roulette, the standard bets all share the same underlying house edge of 2.7%. The game’s payouts are designed so that, over time, a straight-up bet, a split, a street, a corner, a column, or an even-money wager all return the same average percentage to the casino.
Take a couple of quick examples. A split bet, which covers two adjacent numbers, pays 17 to 1, yet it succeeds two times in 37 outcomes. A column bet covers 12 numbers and pays 2 to 1, but it misses when zero lands. The details differ, but the built-in margin is the same.
American roulette increases that margin for all standard bets because of the extra double zero. One exception on the American layout is the five-number bet on 0, 00, 1, 2 and 3, which carries an even higher edge than the rest, making it the least favourable standard option on that wheel.
Some online variants include side bets or bonus features. These can change the edge for that specific wager, which is why the game’s information page might be useful if you want to see how each bet is priced.
Do Roulette Payouts Match the True Odds?
Not quite. As explained earlier, roulette pays out just below the true mathematical odds, and that gap is what creates the house edge.
You can see it across the layout. A straight-up pays 35 to 1 even though the true odds are 36 to 1 on a European wheel. A split pays 17 to 1 instead of the true 18 to 1. A street pays 11 to 1 instead of 12 to 1, and a corner pays 8 to 1 instead of 9 to 1. Even-money bets pay 1 to 1, but they do not win when zero appears. Each example is a small shortfall on the return compared to the probability, and those small shortfalls add up over many spins.
Online and live dealer tables usually follow the same payout schedule for European and American versions, unless the game clearly lists alternative rules.
European vs American Roulette: Which Is Better for Players?
Both versions look similar, but the single zero on European tables means a lower edge. With 37 pockets, the long-term house margin is 2.7%. The American wheel’s extra double zero increases the number of outcomes to 38 and raises the margin to about 5.26%. The payouts for equivalent bets are the same across both versions, which is why that extra pocket makes the difference.
If you prefer a lower house edge, look for European or French tables, which are widely offered in the UK. Some French roulette games apply La Partage or En Prison on even-money bets when zero hits, trimming the edge further on those wagers.
Why the House Edge Matters Over Time
The edge is a long-term average. On any single spin, anything can happen. Over hundreds or thousands of spins, the results converge towards the expected return. On European roulette, the theoretical return to player is 97.3%, which is another way of saying the house expects to retain 2.7% of all stakes in the long run.
To make that concrete, imagine a large number of £1 bets placed across many sessions. Swings will occur in the short term, yet the overall return tends to settle near that 97.3% figure as the sample grows. Casinos set the payouts so this arithmetic holds steady across every bet type and across both physical and online tables.
Digital games use independently tested RNGs to mirror the unpredictability of a physical wheel, and live dealer games rely on standard casino equipment. The structure of the payouts is what ensures the house edge persists, which is how casinos make money on roulette regardless of who is spinning the wheel.
