How are slot machine symbols chosen?

How are slot machine symbols chosen? The short answer

Every modern slot machine, whether it is an online video slot or a fruit machine in a pub, hands the job of choosing symbols to a random number generator. The RNG doesn't think in pictures. It produces numbers, and the game's software maps each number to a position on a reel strip, the long list of symbols that a reel cycles through. Once the position for each reel is fixed, the grid you see is fixed too.

So the honest answer has two layers. Which symbols land on a given spin is chosen at random by the RNG. How often each one can land was chosen months earlier by the game's mathematician, who decided how many times to place each symbol on each strip. That second decision, called weighting, is what makes a top symbol rare and a low-paying symbol common, and it is tied directly to the paytable and the game's return to player.

There is also a design question behind the search: why a game uses cherries, books or fish in the first place. We cover that further down, along with the history of fruit and BAR symbols.

From random number to symbol: the step-by-step chain

The process below applies to online slots and to most electronic gaming machines in UK venues. The exact maths differs from game to game, but the order of events doesn't.

1. You press spin. Your stake is taken from your balance or credits meter.
2. The RNG, which runs continuously, supplies a fresh random number for each reel (or for each position, on some grid games).
3. The software scales each number to the length of that reel's strip, so a number becomes 'stop 37 of 80', for example.
4. The symbols at that stop, plus the ones directly above and below it, become the visible window for that reel.
5. The game compares the finished window with the paytable and works out any win.
6. Only then do the reels animate, slow down and land on the result that was already settled.

Because the outcome is settled in steps two to five, nothing you do while the reels are moving has any effect on which symbols appear. That is also why UK rules can ban slam-stop buttons without changing a single result: stopping early would only shorten the animation. Our page on how a slot machine decides who wins goes through the same chain from the payout side.

Reel strips and weighting: why some slot symbols land more often

Weighting is the single biggest factor in how slot machine symbols are chosen. If a reel strip has 32 positions and the seven appears on two of them, the chance of a seven landing on the payline from that reel is 2 in 32. Put eight cherries on the same strip and a cherry lands four times as often. The RNG treats every stop equally; the designer makes some symbols more likely simply by giving them more stops.

These numbers are invented for illustration, not taken from any real machine, but the logic is exactly how real games work. A three-seven line that turns up once in 4,096 spins can carry a large prize; a three-cherry line that appears once in 64 spins has to pay modestly or the game would hand back more than it takes. That trade-off between frequency and size is what volatility describes.

Reels do not have to be identical, either. A designer can give reel three fewer high symbols than reel one, which is one reason two-symbol 'nearly' lines look common. Different strips are also often used in the base game and in a free spins round, so the feature can feel richer without the base game becoming any more generous.

Virtual reels: how land-based slot machines choose symbols

Physical reels can only hold so many symbols before they become too large for the cabinet. The fix was the virtual reel, patented by the Norwegian mathematician Inge Telnaes in 1984 (US patent 4,448,419, later bought by IGT, according to the Wikipedia history of the slot machine (opens in a new tab)). The RNG picks a stop on a much longer invisible list, and each virtual stop is mapped to a symbol or blank on the real drum.

With 256 virtual stops per reel, a three-reel machine has 256 × 256 × 256 = 16,777,216 possible combinations, far more than any physical drum could produce. The jackpot symbol might be mapped to one virtual stop while the blanks either side of it are mapped to many. The reel then lands on that blank much more often than its physical size would suggest. See virtual reels and weighted reels for worked mappings.

How online slot symbols are chosen on video, Megaways and grid games

Online slots have no physical limit, so strips can be as long as the maths needs. The principle stays the same, but the mechanic changes what the RNG is asked to pick:

• Payline slots such as Book of Dead (Play'n GO, 10 paylines, 5,000x max win) pick one stop per reel and show three rows from each strip.
• Megaways slots such as Bonanza Megaways (Big Time Gaming, up to 117,649 ways) first pick how many symbols each reel shows on that spin, then fill the reel from its strip. Read more on Megaways slot machines.
• Scatter-pays grids such as Gates of Olympus (Pragmatic Play, 6 × 5, 8+ matching symbols anywhere) still draw from reel strips; it is the win rule that ignores lines.
• Cascading games remove winning symbols and drop new ones in from the strip, so each cascade is a continuation of the same pre-settled result.

Special symbols are chosen the same way. A wild or scatter has stops on the strip like any other symbol, sometimes only on certain reels, which is how a designer controls how often a bonus can trigger.

How designers choose which symbols go into a slot machine

Before any maths is done, a studio decides on a theme and a symbol set. Most games follow the same structure: a handful of themed high-paying symbols, a set of low-paying ones (often card ranks), and a few specials that run the features. The paytable then ranks them, and the weighting is tuned until the overall return hits the target RTP.

Card symbols are a nod to the very first machines. Our pages on card royals and high-pay symbols explain why nearly every video slot still uses them as the low tier.

Why slot machines use fruit, bells, BARs and sevens

Many traditional slot machine symbols were chosen for reasons that have nothing to do with maths. The early 1890s poker machine by Sittman and Pitt used 50 playing cards on five drums. Charles Fey's Liberty Bell had three reels with horseshoes, diamonds, spades, hearts and a bell, and three bells paid ten nickels.

Fruit arrived with the Mills Operator Bell, which came with an optional gum-vending attachment. Because the gum was fruit-flavoured, lemons, cherries, oranges and plums went on the reels, and a pictured stick of Bell-Fruit Gum is the usual explanation for the BAR symbol. The cherry and the bell spread as other makers copied the set. Accounts of dates differ between sources, so see our history of fruit machines for how each date is supported.

Are symbols chosen differently on a UK fruit machine?

A pub fruit machine also uses electronic randomness to pick reel positions, but many UK machines are compensated: the software keeps track of how much it has paid against its target percentage and can adjust what it offers. That affects the features offered (nudges, holds, number trails), not some hidden decision about which picture to show next. Category B to C machines must display their theoretical target return, and the Commission's draft technical standards require a machine to say either 'THIS GAME IS RANDOM' or that it is compensated. More on compensated machines.

Using a nudge or hold well can stop you missing a win the machine has offered, but no technique beats the payout percentage built into the machine.

Myths about how slot machine symbols are chosen

• 'The symbols change when you press stop.' The result exists before the reels move. Online, slam-stop is banned in Great Britain anyway.
• 'A machine that just showed two sevens is close to a jackpot.' Each spin is drawn independently; see slot machine near misses.
• 'Symbols are chosen to match your losses.' A random game has no memory of you. Our myths guide covers the 'due' and 'hot machine' ideas.
• 'Bigger bets get better symbols.' Weighting is set in the game's maths, not by your stake, unless the paytable says otherwise (some older games pay extra at top stake).

UK rules that shape how slot symbols are chosen and shown

Game makers supplying Great Britain must have their RNG and games tested by a test house approved by the Gambling Commission, which listed 14 such labs on 2 March 2026 (see the Commission's approved test houses list (opens in a new tab)). Online, the Commission's remote technical standards (opens in a new tab) also require the rules, the chance of winning (RTP or the probability of winning events) and the paytable to be available before you play.

For the broader picture, see UK slot machine rules and our hub of slot machine questions.

Where to see symbol weighting in action (18+)

You can't see a game's reel strips, but you can see their effect: the paytable in the help screen shows how much each symbol pays, and the rarer symbols always pay more. Big Bass Bonanza is a useful example because it is the game PlayOJO's 80 no-wagering spins are played on (new UK customers excluding Northern Ireland, first deposit of at least £10, spins worth 10p each, winnings paid in cash). Coral's offer is 100 spins at 10p on selected games when you deposit and bet £10 on slots (48 hours to accept, valid 7 days, no wagering, some payment methods excluded), and Ladbrokes gives up to 500 spins at 50 a day for 10 days after you play £10 on slots.

All three are for 18+ new customers and terms apply. Because one company runs both Coral and Ladbrokes, read each welcome offer's terms before signing up to the pair. Game lobbies change, so search the casino for a title rather than assuming it is there, and set a deposit limit before you start.

18+. Gambling should be entertainment that costs money, not a way to make it. Decide a budget before you play: plan a slot budget. Free, confidential help: National Gambling Helpline 0808 8020 133.