The d10, properly introduced
There is no ten-faced Platonic solid, so the d10 is a pentagonal trapezohedron: ten kite-shaped faces meeting at two points. It earns its place because we count in tens. Roll two of them and you get a percentile throw, 1 to 100, which is how RPGs have resolved skill checks since the late 1970s. Its faces read 0 through 9, with 0 conventionally counted as ten.
Roll it for: percentile rolls, paired as tens and units; random digits, one at a time; any 1-in-10 decision. And if the d10 isn't the die your game asks for, the full dice roller has the other five.
- 10, numbered 1 to 10
- Pentagonal trapezohedron, not a Platonic solid
- 10% — exactly 1 in 10
- 5.5
- averages 11; totals range 2 to 20
- two 10s in a row: 1 in 100
D10 — frequently asked
A 10-sided die shaped as a pentagonal trapezohedron, the one standard die that is not a Platonic solid. The only die in the standard set that isn't a Platonic solid. Faces are numbered 1 to 10, and on a fair d10 each lands with exactly a 10% chance.
One in 10, or 10%, the same as every other face. Rolling two 10s back to back happens once in 100 attempts. The roller here uses rejection sampling on a cryptographic generator, so those odds hold exactly.
5.5. A fair die averages the midpoint of its range, so 2×d10 averages 11 and 3×d10 averages 16.5. Single rolls are flat: an average result is no more likely than a 10 or a 1.
Percentile rolls, paired as tens and units; Random digits, one at a time; Any 1-in-10 decision. Beyond those, any decision with 10 options maps onto it directly.