Random number generator casino games: how RNG really works

Key facts

A random number generator (RNG) produces numbers that a game maps to outcomes: a roulette pocket, a card or a set of reel stops.
The Australian/New Zealand Gaming Machine National Standard requires RNG results to be statistically independent, uniformly distributed, able to pass recognised statistical tests, and unpredictable.
Scaling is where bias creeps in. In our calculation, mapping a random byte (0 to 255) onto 37 pockets with a simple remainder makes 34 pockets 17% more likely than the other 3. Standards require that bias to be removed.
The UK Gambling Commission's online standard bans compensated games: an RNG game may not adjust results to make up for earlier wins or losses.
A physical wheel is controlled differently: Australian rules set the ball size (17 to 22 mm), the spin direction and a minimum of three or four revolutions.

How a casino random number generator works

A random number generator in a casino game is the part of the software that decides results. It produces a stream of numbers, and the game converts each number it uses into an outcome: a pocket on a virtual roulette wheel, a card from a virtual deck, or a stop position on each reel of a pokie. Nothing else about the game, not the animation, the sound or the near miss, has any say in what you win.

Australia's technical rulebook for gaming machines, the Australian/New Zealand Gaming Machine National Standard, says it in two lines. Game software must generate random symbols or reel stops "from a Random Number Generator (RNG) and mapping algorithm", and it must not determine the outcome of a play until all player options for that play have been made.

The four things an RNG must prove

The national standard (Revision 11, adopted in Tasmania's gaming machine standards from 1 December 2025) sets a single fundamental requirement. RNG results must be able to be proven to:

be statistically independent;
be uniformly distributed over their range;
pass various recognised statistical tests; and
be unpredictable.

The tests it lists include the chi-square test, the equi-distribution (frequency) test, the gap test, the poker test, the coupon collector's test, the permutation test, the run test, the spectral test, serial correlation tests and tests on subsequences. In plain terms, testers check that every number turns up as often as it should, that there are no hidden patterns or repeats, and that each result has nothing to do with the previous one.

Cryptographic strength and seeding

Passing statistics tests is not enough on its own, because a pattern can look random and still be predictable to someone who knows the formula. So the standard says all new RNG implementations should be cryptographically strong, and resistant to three kinds of attack:

Attack	What the standard requires
Direct cryptanalytic	Knowing a sequence of past results must not let anyone predict future ones
Input-based	Nobody can manipulate the inputs to force the RNG into a known state
State compromise	Even if the internal state leaks at one moment, future output stays unpredictable

Seeding, the starting value an RNG works from, must ensure the same sequence of random numbers is never used. Hardware RNGs that sample physical noise are allowed, but they must be monitored for deterioration or malfunction.

The scaling trap, in roulette numbers

This is where a careless RNG would quietly cheat. An RNG produces numbers over a big range, but a roulette wheel has 37 pockets, so the game has to shrink the range. The lazy method is to take the remainder after dividing by 37.

Suppose the RNG produced one random byte, a number from 0 to 255. There are 256 possible values, and 256 is not a multiple of 37 (it is 6 x 37 + 34). In our calculation the remainder method gives:

Pockets	Chances out of 256	Probability	Fair probability
0 to 33 (34 pockets)	7 each	2.73%	2.70%
34, 35, 36 (3 pockets)	6 each	2.34%	2.70%

That is a 17% difference between the favoured and unfavoured pockets. A straight-up bet at 35 to 1 on a favoured pocket would carry a house edge of about 1.6%; on pocket 34, 35 or 36 it would be about 15.6%. Nobody would see it at the table.

The standard closes this hole. When a game scales a number down to a smaller range, "all numbers within the lower range are equally probable", and a number that falls outside the range of equal distribution may be discarded to eliminate bias. In the byte example, that means throwing away 222 to 255 (13.3% of draws) and using only 0 to 221, which is exactly 6 x 37. The UK Gambling Commission's online standard says the same thing in its own words: any scaling must keep the RNG's qualities intact.

No memory, no compensation

The UK Gambling Commission's technical standard for online gambling requires results to be "acceptably random" and states that "Adaptive behaviour (that is, a compensated game) is not permitted." A compensated game would be one that pays more after a cold run or less after a hot one. Its guidance adds that random numbers must be used in the order they are received and not discarded because of adaptive behaviour, and that simulated devices must stay independent: a simulated coin must land heads with probability 0.5 every time.

Australia's standard makes the matching consumer rule: games must provide outcomes that are not dependent on previous outcomes, and must not be misleading, for example through a near miss design. So the "it's due to pay" idea has no mechanism to work through. Our gamblers fallacy guide shows what genuine randomness looks like on a results board, and how pokies work applies the same idea to reels.

RNG roulette versus a real wheel

A physical roulette wheel is a random device too, just a mechanical one, and Australian rules control it closely. Tasmania's approved roulette rules require a 37-compartment wheel and a non-metallic ball between 17 and 22 mm, spun in the opposite direction to the wheel, with a "No Spin" called if the ball is unlikely to complete three revolutions. Victoria's approved casino rules set the minimum at four revolutions.

The UK standard treats physical devices as "mechanical RNGs" and asks for three things: parts made of materials that will not decompose over time, physical properties that are not altered, and no way for players to touch or manipulate the mechanics.

	RNG roulette	Physical wheel (live or in a casino)
Source of randomness	Software or hardware RNG plus mapping	Ball, wheel and spin
Key controls	Statistical tests, cryptographic strength, unbiased scaling	Equipment approval, spin rules, no-spin calls
Speed	As fast as you press	Limited by the spin
House edge (single zero)	2.70%	2.70%

Some games mix the two. Evolution says its Lightning Roulette "combined digital random number generators with the Live Roulette wheel", using an RNG to pick the boosted numbers each round while the ball decides the result. Its First Person games are RNG-based versions of its live tables with the same rules. More on those formats is in our live roulette guide.

Pundit tip: a fair RNG is not a generous one. Randomness decides which result you get; the payout table decides how much the casino keeps. Check the house edge before worrying about the randomness.

RNG casino games and Australian law

The national standard applies to gaming machines in Australian venues, and casino table game rules are approved by regulators: in Victoria, the VGCCC says it must by law approve any rules or changes to table games at the casino. Online casino games are outside that system altogether: under the Interactive Gambling Act 2001, ACMA lists casino-style games, including roulette, as illegal to offer online to people in Australia, and warns that players with illegal operators risk losing their money. Our online roulette Australia page covers what that means for you.

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Frequently asked questions

How does a random number generator work in a casino game?

The RNG produces a stream of numbers, either by software using a cryptographic algorithm, by hardware sampling physical noise, or both. When you play, the game takes a number and maps it to a result, for example pocket 17 on a roulette wheel. Standards require each result to be independent of the last and every outcome to occur at its intended probability.

Are RNG casino games rigged?

Properly built ones are not, and the standards exist to check exactly that. Australia's gaming machine standard lists tests such as chi-square, gap, run and serial correlation tests, and requires mapping that keeps every outcome at its statistical expectation. RNG games still carry a house edge, which comes from the payouts, not from the randomness.

Can you predict an RNG?

Not one built to current standards. Australia's standard says new RNGs should be cryptographically strong, so that knowing past outputs, or even the internal state at one moment, cannot be used to predict future results.

Is live roulette random in the same way as RNG roulette?

It is random by physics rather than software. The ball, wheel and spin are controlled by approved rules; some live games add an RNG on top, such as Evolution's Lightning Roulette, which combines digital random number generators with a live wheel for its multipliers.

Do RNG games run hot and cold?

No. Standards require each result to be independent of the previous ones, and the UK Gambling Commission does not permit games that adapt their results. Streaks on an RNG game are ordinary randomness.