Every dice type explained (d2 to d100)

Ask most people to picture a die and they’ll think of a cube. Tabletop gaming uses a whole family of shapes, most of them the five “Platonic solids” whose faces are all identical — plus a few clever cheats for the numbers geometry won’t give you cleanly. Here’s the full cast.

The everyday dice

A note on the d2 and d3

You rarely buy these — they’re usually improvised. A d2 is just a coin, or a d6 where 1–3 means “low” and 4–6 means “high”. A d3 is most often a d6 with the result halved and rounded up (so 1–2 = 1, 3–4 = 2, 5–6 = 3). True prism-shaped d2 and d3 dice exist, but the fake versions are everywhere.

Why the d10 gets a partner

Two ten-sided dice make a d100. One is printed 00, 10, 20…90 (the tens) and the other 0–9 (the units). Read together they give 1–100, with a double-zero counting as 100. That pairing is why percentile-heavy games like Call of Cthulhu lean on the d10 so hard — more on that in our dice-by-system guide.

The oddities

Beyond the standard set live dice that geometry doesn’t hand over neatly, so makers get inventive:

• d16 — a bipyramid; occasionally used where a range of sixteen is wanted, or as a novelty.
• d24 — often a trapezohedron or tetrakis shape; niche, sometimes used for hours-of-the-day or fractional results.
• d30 — a rhombic triacontahedron, a genuinely useful oddball for tables of thirty entries or big single rolls.
• d100 Zocchihedron — the wild one. Designed by Lou Zocchi, it’s a near-spherical solid with 100 tiny faces that gives a true single-die 1–100. It rolls for ages and is more curiosity than workhorse, but it’s a beloved piece of dice history. Physical ones are also measurably biased — here is why, and how ours avoids it.

The opposite-faces rule

Pick up almost any standard die and add the number on top to the number directly underneath. On a well-made die, the two opposite faces sum to one more than the total number of sides:

• d6: opposite faces sum to 7 (1–6, 2–5, 3–4)
• d8: sum to 9
• d12: sum to 13
• d20: sum to 21

The reason is balance: pairing high with low across the die spreads the material and pip-weight as evenly as possible, which helps fairness. It also gives you a quick knock-off check — if a die’s opposite faces don’t add up, be suspicious. (For the deeper story on balance, see how dice are made fair.)

The d10 exception

The d10 breaks the pattern because it’s numbered 0–9 rather than 1–10. Its opposite faces sum to 9, not 11 — a direct consequence of starting at zero. It’s the one standard die where the “n+1” rule doesn’t apply, so don’t use that test to judge a d10.

Is a d100 actually fair?

Short answer: a physical Zocchihedron is not, and that is well documented. The real Zocchihedron is documented as measurably unfair: White Dwarf rolled one 5,164 times and found numbers above 93 and below 8 came up significantly less often, because the faces near the poles are packed closer together. The magazine Gateways tested one too and found that on a hard surface it tends to roll along its equator, favouring the numbers around the middle of the die. Lou Zocchi went on to fill later models with free-falling weights to make them settle sooner, which tells you the problem was real.

It is not a manufacturing fault so much as geometry. A die is fair when every face is identical, which is why a d6, d8, d12 and d20 can be trusted: spin any of them around and it looks the same. You cannot do that with a hundred faces. The only convex solid with 100 identical faces is a 50-gonal trapezohedron — picture your d10 with fifty kites per end instead of five. It is a spinning top, its faces are slivers too narrow to print a legible number on, and nobody would want to roll it. A near-spherical d100 must therefore use faces of slightly different sizes, and different sizes mean different odds.

How Dice Drop’s d100 works

We wanted the die people actually picture — the golf ball — without inheriting its bias. So Dice Drop does not read the number off whichever face the ball happens to stop on. It draws the number first, uniformly from 1 to 100, and then turns the ball onto that face as it slows and settles.

• The draw uses your device’s cryptographic random number generator — the same source that throws every other die in Dice Drop, not a reused shuffle or a seeded sequence.
• The tumble is genuine physics: real collisions, real friction, real settling. What is fixed in advance is only which face wins, exactly as a fair die would have decided it anyway.
• Opposite faces sum to 101 throughout, following the same balance convention as every other die in the set.
• The winning number is also turned upright as it settles, so you can read it without tilting your head.

We test it rather than assert it. Two checks run against the shipped code: 200,000 draws through the app’s own randomness give a chi-squared of 108.45 against a 99.9% critical value of 148.23 — statistically indistinguishable from a flat 1–100 — and the two ranges White Dwarf found to be rare on a real Zocchihedron came in at 13,993 and 13,931 against 14,000 expected. A second check rolls the die through the real physics and confirms the number reported is always the number left facing up.

If you would rather have dice do the deciding, Dice Drop also offers d%: the traditional percentile pair, a tens die reading 00–90 and a units die reading 0–9, giving 1–100 with 00 + 0 read as 100. Those are two ordinary ten-sided dice, each fair by its own symmetry, and their result is read off the faces exactly like every other roll.

Which do you actually need?

For nearly everything, the seven-dice polyhedral set is plenty. The oddities are for collectors, custom random tables and the joy of watching a Zocchihedron roll across the table for a full ten seconds. The oddities stay oddities, mind: Dice Drop rolls the standard set, not a d16, d24 or d30. If your table needs one of those, a physical die or a general-purpose random-number roller is still the answer.

Keep reading: the best dice for every RPG system — which of these you’ll actually roll at your table.