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How the roulette RNG works, and what the certificate means
An RNG roulette table has no wheel, no ball and no dealer. It has a piece of software that produces a number from 0 to 36 each time you press spin, and an animation that shows a wheel landing on it. Everything about whether the game is fair comes down to that piece of software and who has checked it. Here is how it works and what the checking covers.
What the RNG does
A random number generator is an algorithm that produces a stream of numbers with no detectable pattern. Modern casino RNGs are seeded from unpredictable physical sources, such as hardware noise or timing jitter, and then run a cryptographic algorithm so that past outputs give no information about future ones. For roulette, each output is mapped to one of 37 pockets with equal probability. The mapping is the easy part; the quality of the stream is what the labs test.
When the result is decided
At the moment you press spin, or the moment the betting window closes on an auto-spin table. The ball animation that follows is a presentation of a result already stored. This feels suspicious to some players, as if the game "knows" before you see it. It does, in the same way a shuffled deck knows the next card before it is turned over. Knowing is not influencing. The result was random when it was generated and the animation cannot change it.
What the testing lab checks
Independent laboratories, named in the game's help screen or the site's footer, test the RNG and the game around it. The tests include:
- Distribution. Over millions of simulated spins, each pocket should appear 1/37 of the time within statistical tolerance.
- Independence. No correlation between one result and the next, or any earlier one.
- Unpredictability. The output cannot be inferred from previous outputs or from timing.
- Payout table. The game pays exactly what its rules state for every bet.
- Return to player. The overall RTP, which for a fair single-zero table is 97.30%, matches the maths.
The certificate names the game version. Any change to the game needs a new certificate.
What the RTP figure certifies
97.30% means that, over a very large number of spins, the game returns £97.30 for every £100 staked, across all bets. It is the mirror of the 2.70% house edge and it follows directly from 37 pockets and a 35:1 straight-up. It does not mean you get 97.30% back in a session; a session of 100 spins can finish anywhere from 60% to 140% of stakes by chance. The figure describes the game, not the night. For how that plays out differently on an RNG table and a live one at the same stake, RouletteFinder has the side-by-side.
What the RNG cannot do
It cannot see who is betting or how much. The result is generated independently of the bets on the table; the game then settles bets against it. A certified RNG has no input from the betting layout, which is the technical reason "the game knows I bet on red" is impossible.
What to look for
A named testing lab. A stated RTP of 97.30% for European or French tables, 94.74% for American. A game version number in the help screen. Those three things mean the software has been through the process above. Their absence means you are on an untested game, and that is a different site from the one this page is about.
Frequently asked
- Is the roulette result decided before the wheel spins on screen?
Yes. The RNG produces the result the instant you press spin; the animation is a display of a decision already made. That is normal and does not affect fairness, because the result was random when generated.
- Can a casino change the RTP of a roulette game?
Not on a certified table. The game logic is the provider's and the certificate covers a specific version. Operators cannot edit the payout table of a roulette game the way slot RTPs sometimes come in several configured versions.