How To Calculate Probability in Roulette - Best Advices

  • Written by Martina Maritato
Here at Bet and Skill we love a spin of the roulette wheel and know all there is to know about the popular casino game. Wanna know how to calculate probability in roulette? Below you’ll find our top tips on how to calculate your chances and win at the roulette table.

Roulette is very simple game to understand. You place a bet on where you think the ball will land and if it does, you win!

Of course, the chances of the ball landing on where you’ve placed your chips can vary dramatically from a one in 37 chance to a 50% chance. But how do you calculate this probability.

The Roulette Table 


Let’s start with the table itself. On a roulette wheel there are either 37 or 38 numbers depending on whether you’re playing American or European Roulette. The numbers range from zero to 36, with a 00 on the American wheel.

The American Wheel has an extra edge to the casino so it’s always worth playing European.

Across the table you’ll find every number as well as a number of Outside bets. These are the spots where you can bet on Odds and Evens, Red or Black and various lines and sections of the table.

You’ll find 18 red numbers and 18 black giving an even chance of the ball landing on red or black. Equally, you’ll find the same number of odd numbers and even.

The zero, and double zero, stand alone and basically unless you bet on it gives the house the edge.

You can place bets on any number as well as many other variants including four numbers (corner bet), such as has been done in the image above with 22, 23, 25 and 26.

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Roulette Table Probabilities
The probabilities vary when it comes to betting on the roulette table.

Betting on Outside Bets will give you a higher chance of winning although does also have a lower payout.

With Outside Bets you’ll usually have around a one in two or one in three chance of winning. These are the following:

Odds/Evens: 48.65% chance of winning. Pays out even money.

Red/Black: 48.65% chance of winning. Pays out even money.

1-18/19-36: 48.65% chance of winning. Pays out even money.

Because the chance of winning is 18/37, this gives you almost a 50% chance of winning your bet by placing these outside bets.

Other Outside Bets and their payouts include:

Column: 32.4% chance of winning. Pays out 2/1.

Dozen: 32.4% chance of winning. Pays out 2/1.

Inside bets have much longer odds as the percentages can be as large as a one in 37 shot.

Below you’ll find some of the more common inside bets and their odds and payout:

One Number: 2.7% chance of winning. Pays out 35/1.

Split: 5.4% chance of winning. Pays out 17/1.

Street: 8.1% chance of winning. Pays out 11/1.

Corner: 10.8% chance of winning. Pays out 8/1.

Six Line: 16.2% chance of winning. Pays out 5/1.

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Calculating Probabilities
Calculating probabilities in roulette is relatively easy and simply involves using the fraction and dividing and multiplying accordingly. It’s basic school mathematics.

So for example, let’s say you wanted to place a bet on red you would use the following formula:

(18/37) x 100

This would give you the percentage chance of you winning. There are 18 reds out of 37 numbers on the table which gives a decimal of 0.4865. Multiply that by 100 to gain the percentage and it’s 48.65%.

You can do this with any probability on a roulette wheel. However, when it comes to working out sequences it’s a little more complex.

Let’s say you wanted to work out the chance of the ball landing on red twice in a row. To work out that you would need to use the following formula:

(18/37 x 18/37) x 100

This would work out at around a 24% chance of happening and ultimately just involved multiplying the fractional odds with each other, and then multiplying by 100 to get the percentage.

You can do this as many times as you want and can forecast a sequence as long as you need to work out the chances of that particular sequence winning.

Where Can I Put Probabilities Into Practice?  

Naturally, once you’ve worked out the probabilities of the roulette table you’re going to want to put into action.

There are dozens of fantastic online casinos to play roulette with, many offering free spins to get started.

Head over to our online casinos page to find all the very best casinos to play roulette with and get in depth reviews on their gameplay and casino promotions.

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