Pick up a handful of dice from a board game shelf and you’ll find more shapes than you’d expect: pyramids, cubes, a two-tone ball that looks like a golf ball with opinions. These are all different dice types, and each one exists for a reason. Some are built for tiny decisions, some for big swings of luck, and one is mostly there because someone wanted to see if it could be done.

Let’s walk through the lot, from the smallest die to the biggest. The letter “d” just means “die”, and the number after it is how many sides it has, so a d6 is the ordinary six-sided one you already know.

What makes a die fair in the first place?

A die is fair when every face has exactly the same chance of landing on top. The easiest way to get that is a shape where every face is identical, so none of them can be favoured.

Five shapes manage this perfectly: the pyramid, the cube, and three others with 8, 12 and 20 faces. That’s why the d4, d6, d8, d12 and d20 are the classics. Other dice, like the d10, cheat a little by using faces that are all the same as each other but not quite as tidy. They still roll fairly. Which brings us to the very smallest dice.

The d2 and d3: smaller than they look

A d2 is simply a coin. Heads is one, tails is two, and you can toss one in the Flip a Coin app when you only have two options.

The d3 is a bit of a trick. Real three-sided dice are rare, so most players roll a d6 and halve it: 1 or 2 counts as one, 3 or 4 as two, 5 or 6 as three. Same odds, no special shape needed. It turns up in games that want a small, gentle bump, like “gain 1 to 3 points”.

The d4: the pyramid you’ll step on

The four-sided die is a pyramid, and it’s the odd one out because there’s no “top face” when it lands. You read the number at the point or along the bottom edge, depending on how it’s printed.

Its low numbers make it a favourite for small damage in role-playing games, like a thrown dagger. It also has a reputation as the most painful thing to step on in the dark, and every tabletop player has a story about it.

The d6: the one everybody knows

The cube is the dice type that built the world of board games. Monopoly, Ludo, Risk, Yahtzee and countless others run on it. Fun detail: on a standard die, opposite faces always add up to seven.

Roll two together and you get something interesting. Totals aren’t equally likely, because 7 can be made six different ways while 2 can only be made one way. That’s why 7 shows up so often in games with two dice. It’s worth remembering before you bet on a 12.

The d8, d10 and d12: the middle of the set

These three sit between the small dice and the big one, and they do the everyday work in tabletop games.

The d8 is an eight-faced diamond, often used for medium weapons or healing. The d12 has twelve five-sided faces and feels chunky in the hand. It’s usually reserved for the big, heavy hits.

The d10 is the odd shape of the family, a kite-faced spinning-top of a die. It’s normally numbered 0 to 9, which means a zero counts as ten in some games and as zero in others. Always check the rulebook before you celebrate.

The d20: the star of the show

If one die has a fan club, it’s this one. The twenty-sided die is the heart of Dungeons & Dragons and plenty of games like it. You roll it to see whether you succeed at something risky: swinging a sword, picking a lock, talking your way past a guard.

Because every number from 1 to 20 has an equal 5% chance, the d20 feels dramatic in a way other dice don’t. Rolling a 20 is cheered around the table, and rolling a 1 is groaned at just as loudly. You can try it yourself with the Roll a Dice tool, which also handles rolling several dice at once with modifiers.

The d30 and other rare oddities

Beyond the standard set there’s a whole shelf of unusual dice. The d30 is a real thing: a chunky shape made of thirty diamond-shaped faces. Some games that use unusual dice, such as Dungeon Crawl Classics, deliberately throw in odd sizes like the d3, d5, d7 and d30 to add variety.

You won’t need one for most games, which is exactly why they’re fun to own. If you want to roll something unusual online, the dice tool lets you choose a custom die with any number of faces, and the Random Number Generator covers any range at all.

The d100 and the Zocchihedron

Rolling a number from 1 to 100 is called a percentile roll, and it’s used when a game wants fine-grained odds, like a 37% chance of something happening. Most players do it with two d10s: one gives the tens, the other the units. Roll a 4 and a 7 and you’ve got 47. Two zeroes mean 100.

Then there’s the showpiece: the Zocchihedron, a single die with a hundred sides, invented by game designer Lou Zocchi in the 1980s. It doesn’t look like other dice. It’s a small ball covered in tiny numbered flat spots, and when you throw it, it bounces and rolls for a surprisingly long time before settling.

It’s not a true polyhedron the way a d20 is, and people still argue about whether it’s as fair as two d10s. Many players buy one for the sheer joy of it, then go back to the pair of d10s for serious play. A real 100-sided shape would be a kind of spiked ball that rolls almost forever, which tells you why the two-dice trick caught on.

Choosing the right dice type for the job

Here’s a rough rule of thumb. Fewer sides means smaller, steadier results, and more sides means bigger swings. A d4 is for a tap on the shoulder. A d20 is for the moment of truth. Percentile dice are for when you need to be precise.

If you’re ever unsure which dice types suit a game, check its rulebook first. Designers choose each die carefully.

Roll every dice type online

You can try almost everything in this guide without owning a single die. The Roll a Dice tool rolls d4, d6, d8, d10, d12, d20 and d100, plus custom dice, and every roll uses the same secure randomness we explain in Is this wheel actually random?. So whether you pick a coin-like d2, a classic d20 or a chaotic Zocchihedron-style d100, every face has a truly equal chance. Have a go, and see which of these dice types becomes your favourite.