The d20, properly introduced
Twenty-sided dice are over two thousand years old. The Metropolitan Museum of Art holds a serpentine d20 from Ptolemaic Egypt, its faces carved with Greek letters, and similar icosahedra turn up across the Roman world. The modern one was rescued from obscurity in 1974, when Dungeons & Dragons made it the game's central resolution die. Rolling a natural 20 has since escaped the hobby entirely and become shorthand for perfect luck.
Roll it for: attack rolls, saving throws, the whole d20 system; a 5% granularity for anything; settling arguments with maximum drama. And if the d20 isn't the die your game asks for, the full dice roller has the other five.
- 20, numbered 1 to 20
- Icosahedron, a Platonic solid
- 5% — exactly 1 in 20
- 10.5
- averages 21; totals range 2 to 40
- two 20s in a row: 1 in 400
D20 — frequently asked
A 20-sided die shaped as a icosahedron, one of the five Platonic solids. Twenty triangles, and the most famous die in gaming. Faces are numbered 1 to 20, and on a fair d20 each lands with exactly a 5% chance.
One in 20, or 5%, the same as every other face. Rolling two 20s back to back happens once in 400 attempts. The roller here uses rejection sampling on a cryptographic generator, so those odds hold exactly.
10.5. A fair die averages the midpoint of its range, so 2×d20 averages 21 and 3×d20 averages 31.5. Single rolls are flat: an average result is no more likely than a 20 or a 1.
Attack rolls, saving throws, the whole d20 System; A 5% granularity for anything; Settling arguments with maximum drama. Beyond those, any decision with 20 options maps onto it directly.