Why Roulette Has 0 and 00: The One-Number Difference That Changes Every Bet

Written by Stephen Tabone for GlobalCasinoGames.com | Based on my own analysis and research, and fact-checked against established roulette probability, official gaming rules and published historical sources on single-zero and double-zero roulette | Last reviewed: 15 September 2026

I find it fascinating that the smallest number on the roulette wheel carries the biggest explanation of how the game works.

Questions such as “Why is there a zero in roulette?”, “What are the odds of hitting 00?” and “What happens if I bet on one number?” may sound different, but they all lead back to the same principle.

The 0 and 00 are not decorative additions. They are the pockets that transform roulette from a collection of apparently fair bets into a casino game with a mathematical house advantage.

Why Is There a 0 and 00 in Roulette?

Historically, detailed descriptions of roulette in Paris around the beginning of the nineteenth century already included both 0 and 00 as spaces favouring the bank.

In the 1840s, François and Louis Blanc commercialised a single-zero version of roulette in Bad Homburg. Removing the double zero gave players a better mathematical game than competing double-zero wheels. It was not generosity; it was clever commercial positioning.

Single-zero roulette subsequently became strongly associated with Europe and Monte Carlo, while double-zero roulette remained the dominant American format.

I examine that development more fully in The History of Roulette: Who Invented It and How It Became a Global Game. What interests me here is what that historical difference does to every modern roulette wager.

What Does One Extra Number Change?

Roulette has 36 ordinary numbers, from 1 to 36. A winning straight-up number pays 35 to 1.

On a theoretical wheel containing only those 36 numbers, that payout would be fair. A player would win on one number and lose on the other 35.

Real roulette adds at least one more result:

The standard payouts do not increase when another zero is added. That is where the casino advantage enters the game.

What Are the Odds of Hitting 00—or Any One Number?

On a fair American double-zero wheel, the probability of hitting 00 is 1 in 38, or approximately 2.63%.

However, 00 is not individually more likely than 17, 23 or any other pocket. Every exact number has the same 1-in-38 probability on that wheel.

On European single-zero roulette, the chance of hitting one selected number is 1 in 37, or approximately 2.70%.

The probability of losing a single-number bet is therefore:

• 36 in 37, or 97.30%, on a single-zero wheel
• 37 in 38, or 97.37%, on a double-zero wheel

That sounds severe, but losing probability and house edge are not the same measurement. The 35-to-1 payout compensates for many losing spins. The house edge measures the average mathematical cost after both the probability and payout have been considered.

This distinction is important because a bet can lose frequently while still producing a much smaller expected percentage loss over the long term.

Why Are Red, Black, Odd and Even Not True 50/50 Bets?

The six familiar even-money bets are Red, Black, Odd, Even, Low and High. Each covers 18 ordinary numbers and pays 1 to 1.

On a European wheel, Red wins on 18 pockets and loses on 19 because zero is green. The winning probability is therefore:

18 ÷ 37 = 48.65%

On an American wheel, Red still covers only 18 pockets, but it loses to the other colour, 0 and 00:

18 ÷ 38 = 47.37%

The same calculations apply to Black, Odd, Even, Low and High.

If someone says they are betting separately on all 18 odd numbers, the hit probability remains the same as the outside Odd bet: 18 covered pockets. Assuming equal total stakes and standard payouts, spreading chips across all 18 odd numbers produces the same basic mathematical relationship in a more complicated form.

If Zero Does Not Appear, Was the Bet Really 50/50?

This is where roulette probability becomes particularly interesting.

If I look backwards after a European spin and know that zero did not appear, there were effectively 36 remaining possibilities: 18 red and 18 black. Within that restricted group, Red and Black divide the outcomes exactly 50/50.

The same is true on an American wheel if I already know that neither 0 nor 00 occurred.

However, that is conditional probability viewed with hindsight. Before the ball lands, the player cannot remove zero from the wheel. The real pre-spin probability remains 18 in 37 on European roulette or 18 in 38 on American roulette.

Zero may not appear during a particular session. That does not mean its risk was absent. The player paid for its presence every time an even-money bet was placed.

Do Previous Losses Improve the Next Bet?

Suppose someone loses four consecutive bets on Red. What are the odds of winning on the fifth attempt?

They remain 18 in 37, or 48.65%, on a fair single-zero wheel.

The four previous losses may affect the bankroll and the player’s emotions, but they do not alter the next spin’s mathematical probability. Black is not required to compensate Red, and Red is not required to recover because it has been losing.

This is why I separate outcome probability from staking strategy. Increasing the fifth stake may change the financial result if it wins, but it does not make Red more likely to appear.

What Are the Odds of the Same Number Appearing Twice?

Once any number has landed on a European wheel, the chance that the following spin repeats it is 1 in 37.

That is different from naming one particular number before both spins. Predicting, for example, 17 followed by another 17 has a probability of:

1 ÷ 37 × 1 ÷ 37 = 1 in 1,369

Repeating numbers attract attention because they look extraordinary. Nevertheless, immediate repeats are a normal feature of random sequences. The previous result remains one of the 37 available possibilities on the next spin.

Why Single Zero and the Half-Back Rule Matter

If I am comparing roulette tables, I begin with the number of green pockets. A single-zero wheel is mathematically preferable to double-zero or triple-zero roulette.

If I intend to play even-money bets, I also check for La Partage.

Under La Partage, when zero lands on Red, Black, Odd, Even, Low or High, only half the stake is lost. This reduces the effective house edge on those qualifying bets from 2.70% to approximately 1.35%.

En Prison approaches the zero result differently by holding the wager for another spin under the published table rules. Some American games may offer a Surrender-style half-back rule, but players should never assume that protection exists. It must be confirmed in the rules before betting.

These protections normally apply only to even-money bets—not to dozens, columns or straight-up numbers.

One Number Explains the Entire Roulette Wheel

The more I study roulette, the more I return to one basic question:

How many pockets sit outside the numbers 1 to 36?

That question tells me the probability of hitting one number, why even-money bets are not genuine coin tosses, how much the house edge costs and whether a supposedly attractive roulette table is worth considering.

Zero is just one pocket, but mathematically it changes every standard bet around it. Double zero changes those bets again.

For the complete breakdown of green pockets, payouts, La Partage, En Prison and the cost of additional zeros, read Roulette Zero Explained: Green Zero, House Edge, Odds and Payouts on the Global Casino Games website.

The wheel may appear to contain dozens of different betting questions. In reality, many of them can be understood by studying just one number.