Double Stacks is a 5×3 video slot from NetEnt that blends the look of a classic fruit machine with a modern stacking twist. Fruits, a bell, BAR symbols, lucky sevens and a bright diamond share the reels, but the real hook is the Double Stacks feature: when a full stack of identical high-paying symbols lands on a single reel, those symbols double and count twice on any active line.
Released in September 2018, the game uses 10 fixed paylines, a medium volatility profile and an RTP of 96.10%. Bets scale from small stakes upward, which suits casual play, and the maximum win of 1,700x the total bet is primarily driven by the Free Spins round with stacked Wilds.
Gameplay, Grid and Paylines
The slot runs on a five-reel, three-row grid with ten fixed paylines that cannot be switched off individually. Wins form when identical symbols land on consecutive reels starting from the leftmost reel, following the standard left-to-right rule. The betting panel is simple: a bet level from 1 to 10, a coin value, and the Spin button flanked by "Auto Play" and "Max Bet" options.
Only the highest win per line is paid, and a line requires symbols to appear in succession from the leftmost reel to the rightmost. All ten lines run left to right, and malfunction voids all pays and plays. A single line costs 10 coins, so a base bet at level 1 and coin value R0.10 equals R1 per spin across all ten lines.
Symbols and Paytable
Two tiers of icons appear on the reels. The low-paying group keeps the fruit-machine spirit alive with cherries, lemons, plums and a watermelon, all paying the same amounts. The high-paying group is formed by the golden bell, the classic red BAR, the flaming 7 and a cyan diamond as the top-paying icon. A glowing yellow star acts as the Wild and substitutes for every symbol except the Scatter, while the Scatter itself triggers Free Spins.
Values in the table below are shown in coins for a standard 10-coin line bet (level 1, coin value R0.10 — one payline equals R1).
| Symbol | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|
| Diamond | 15 | 30 | 45 | 90 | 120 | 175 | 250 | 1000 |
| 7 | 10 | 20 | 40 | 80 | 100 | 150 | 175 | 500 |
| BAR | 10 | 15 | 30 | 60 | 70 | 90 | 120 | 250 |
| Bell | 5 | 10 | 20 | 30 | 50 | 60 | 80 | 100 |
| Cherry | 5 | 10 | 20 | 30 | 40 | 50 | 60 | — |
| Plum | 5 | 10 | 20 | 30 | 40 | 50 | 60 | — |
| Lemon | 5 | 10 | 20 | 30 | 40 | 50 | 60 | — |
| Watermelon | 5 | 10 | 20 | 30 | 40 | 50 | 60 | — |
The 10-symbol column applies only to the four premium icons — this is the payout when a line is fully filled with doubled stacked symbols. Fruit caps at a 9-symbol count, which is only reachable through stacked Wild substitutions during Free Spins.
The Double Stacks Feature
The core mechanic that gives the slot its name activates whenever a single reel stops fully covered by identical high-paying symbols — diamond, 7, BAR or bell. Once the reel locks in, all three visible positions double, and each symbol is counted twice during line evaluation.
This rule turns a standard five-symbol line into a potential ten-symbol line. That is why the paytable lists special values for 10 matching symbols on the four premium icons, including 1,000 coins for a fully doubled diamond line. If two or more reels produce full stacks at once, the doubled counts compound across the payline and lead to the biggest base-game payouts.
One important detail: only the four top symbols can appear stacked in the base game. Cherries, lemons, plums and watermelons always land individually and keep their normal one-per-reel count.
Free Spins with Stacked Wilds
Three or more Scatters appearing anywhere on the reels launch the Free Spins round. The number of spins awarded is fixed by the trigger size:
-
3 Scatters — 5 Free Spins
4 Scatters — 15 Free Spins
5 Scatters — 30 Free Spins
During the round, the four highest-paying symbols keep their ability to appear in full-reel stacks, and Wild stars are added to the reel strips. Wilds can arrive as single icons or as stacked positions, and they can also double under the Double Stacks rule when an entire reel fills with Wilds.
Free Spins can be re-triggered mid-round. Two or more Scatters landing during the feature add extra spins: 2 Scatters give 2 spins, 3 give 5, 4 give 15, and 5 Scatters add 30 spins to the remaining counter.
Bet Sizing and Maximum Win
Bets scale through two controls — bet level (1 to 10) and coin value. A single payline always costs 10 coins regardless of level, so the minimum bet at level 1 and coin value R0.10 works out to R1 per spin across all ten lines. The maximum bet caps at R200, giving a wide range for any session size.
The maximum win is 1,700x the total bet. The jackpot-style display at the top of the screen also shows individual symbol caps for the case when the entire reel area is filled with a single symbol: 10,000 for the diamond, 5,000 for the 7, 2,500 for BAR and 1,000 for the bell.
Demo Play and Practice Sessions
Testing the slot in free-play mode is useful for a game built around one specific mechanic. The Double Stacks demo runs identically to the paid version, uses play coins instead of real funds, and makes it easy to see how often full-reel stacks actually form at medium volatility. Most NetEnt-licensed casinos offer a browser-based demo directly on the game page, usually labelled "Play for fun" or "Demo" next to the main launch button.
A short practice session is enough to feel the rhythm of the game: fruit wins arrive steadily thanks to the 16% hit frequency, while doubled stacks and Scatter triggers are less frequent but deliver most of the variance.
Payout Mechanics & Math Profile
Double Stacks is a line-pay slot on a 5×3 grid with only 10 fixed paylines, which is a narrow pool of winning ways for a modern release. That narrowness shapes how the 96.10% RTP is distributed across the reels. In a traditional payline game, base-game RTP is spread fairly evenly across symbol tiers, but here the picture is different.
A large share of RTP is pushed into the Double Stacks event because the 10-symbol payouts for the four premium icons are disproportionately large compared to their 5-symbol values. A normal 5-symbol diamond line pays 45 coins, while a fully doubled 10-symbol diamond line pays 1,000 coins — roughly a 22x jump on what the math engine treats as the same line with one fully stacked reel. The same ratio holds for BAR, 7 and bell. Most of the base-game variance therefore depends on how often a single reel lands fully filled with one of these four symbols, not on how often Scatters trigger the bonus.
The stacking rule also has a structural side-effect. Low-paying fruit cannot stack at all, so it generates frequent but small wins that sustain the 16% hit frequency and give the session a steady feel. The real variance lives entirely in the four stackable symbols and in the Free Spins round, where stacked Wilds are added on top and can also double.
Free Spins contribute less per trigger than one might expect, because the round is short at 3 Scatters (just 5 spins), and the overall 1,700x cap limits how far stacking interactions can push a single sequence. There is no bonus buy and no ante-bet feature in the Double Stacks demo or real-money mode, so the only way to reach Free Spins is by hitting the Scatters organically.
| Metric | Structural Value | Mathematical Impact |
|---|---|---|
| Grid layout | 5×3, 10 fixed paylines | Narrow payline pool concentrates RTP on the leftmost-reel sequence |
| Stackable symbols | 4 out of 8 paying symbols | Fruit provides baseline hit rate, premiums carry the variance |
| Doubling multiplier | ×2 per fully stacked reel | Converts a 5-symbol line into a 10-symbol payout with non-linear payout growth |
| Stack Concentration Ratio (Custom) | 50% of paying symbols able to stack | Most top-tier RTP is gated behind the full-reel stacking event on premium icons |