Polyhedral Dice Explained for New Players

What are polyhedral dice?

A polyhedron is any 3D shape with flat faces and straight edges. "Polyhedral dice" is the name gamers use for the full family of dice beyond the ordinary six-sided cube: four, eight, ten, twelve and twenty sides. They became standard with Dungeons & Dragons in the 1970s and are now used in most tabletop role-playing games.

New players usually meet them as a seven-die set. The one you will roll most is the twenty-sided die; you can practice with the d20 roller before your first session. For a quick rundown of what each die does in play, see D&D dice names.

Why are most dice Platonic solids?

For a die to be fair, every face must have the same chance of ending up on top. The simplest way to guarantee that is to make every face identical. Shapes whose faces are all the same regular polygon, with the same number of faces meeting at every corner, are called Platonic solids. There are exactly five of them, and they map straight onto five of your dice.

The shapes are named after the Greek philosopher Plato, who wrote about them, although they were studied by mathematicians before and after him.

Why is the d10 a different shape?

There is no Platonic solid with ten faces, so the d10 uses a different trick. It is a pentagonal trapezohedron: two five-sided "caps" of kite-shaped faces, joined with a twist so the kites of the top cap fit between the kites of the bottom cap. Every face is the same kite, and the shape looks the same from every face, so each number is still equally likely.

Shapes like this, where every face is equivalent even though the faces are not regular polygons, are called isohedral (face-transitive) shapes. The same idea is used for many novelty dice. The percentile die in your set is a second pentagonal trapezohedron marked in tens.

How do you read each polyhedral die?

Most dice show the result on the face pointing straight up. Two dice in the set work differently.

• d4: a tetrahedron lands with a point facing up, so there is no top face. On the most common style, each face has three numbers, one near each corner; read the number that sits at the top point (it is the same on all three faces you can see). Some d4s instead print the number along the bottom edge of each face.
• d6, d8, d12, d20: read the face on top. If a 6 and a 9 could be confused, look for the dot or underline beneath one of them.
• d10: read the top face. It is usually numbered 0 to 9, and a 0 means 10 (except when used for percentile rolls).
• Percentile die: marked 00, 10, 20 up to 90. Roll it with a d10: the percentile die gives the tens and the d10 gives the ones, so 30 and 7 is 37. A 00 and a 0 together mean 100. See percentile dice for more examples.

What if a die lands tilted?

If a die leans against a book or lands on the edge of a tray, the usual table rule is to reroll it. Agree on this with your group before the game so nobody argues mid-combat.

How do you keep polyhedral dice in good shape?

Dice are cheap and tough, but a little care keeps them readable and fair for years.

• Use a tray: a felt-lined dice tray or box stops dice from flying off the table and protects both the dice and the furniture.
• Be careful with metal and gemstone dice: heavy dice can chip each other and dent wooden tables, and stone dice can crack if dropped on hard floors. Roll them only onto a soft surface.
• Store them separately: soft-material dice like resin can scratch when they rattle against metal dice in the same bag.
• Avoid heat: do not leave plastic or resin dice in direct sun or a hot car, where they can soften or warp.
• Clean gently: wipe with a damp cloth and mild soap; harsh solvents can wash out the painted numbers.

Are polyhedral dice actually fair?

No physical die is perfectly fair, but most are fair enough for play. Small flaws come from how dice are made: air bubbles trapped inside, faces that are slightly different sizes, or edges rounded unevenly in tumbling. The deeper the numbers are carved, the more material is removed from high-numbered faces, although the effect is usually very small.

Ways to check a die

1. Look at it closely. Visible bubbles or lopsided faces are a red flag.
2. Try the salt water test on plastic or resin dice: dissolve salt in warm water until the die floats, then spin it and let it settle several times. If the same few numbers keep coming up, the die may be weighted toward them. Metal dice will not float, so this test does not apply to them.
3. Roll it many times and count the results. You need hundreds of rolls to spot a small bias, since short streaks happen even with a fair die.

Precision dice, with sharp edges and numbers filled flush with paint, are made to tighter tolerances, but they cost more. If fairness worries you, an online roller avoids the physical issue entirely. Ours picks each number with the browser's crypto.getRandomValues, so every face is equally likely.

Do new players need to buy polyhedral dice?

Not right away. Many groups share dice at the first session, and an online roller covers every die you need. Most players buy their own set once they know they enjoy the game, partly because choosing dice is part of the fun. For a breakdown of what to get and which classes need extra dice, read how many dice are in a D&D set.

FAQ

What does polyhedral mean?

A polyhedron is a 3D solid with flat faces, straight edges and sharp corners. Polyhedral dice are simply dice built from these shapes, such as the 20-faced icosahedron.

How do you read a d4?

A d4 has no top face, so you read the number at the top point, or along the bottom edge on some styles. On the common style, the same number appears near the top corner on each of the three visible faces.

Are metal dice fair?

Metal dice can be as fair as plastic ones if they are made accurately, but they are heavy and can dent wooden tables. Roll them into a dice tray.

How can I tell if my dice are fair?

The common hobby test is to float a plastic die in salt water and spin it several times; if the same number keeps floating to the top, the die is off-balance. It does not work for metal dice.

Related

• Roll a d20
• D&D Dice Names: What Each of the 7 Dice Is Used For
• How Many Dice Are in a D&D Set (and Do You Need Your Own)?
• Percentile Dice: How to Roll a d100 with Two d10s