d20s

A twenty-sided die, or d20, is a polyhedral die used in tabletop role-playing games. It is an icosahedron, a shape with 20 triangular faces. Each face bears a single integer from 1 to 20, typically arranged so that opposite faces sum to 21. The d20 is commonly sold as part of a standard dice set that also includes d4, d6, d8, d10, and d12. This shape provides a relatively uniform distribution across its range of values and is valued for its compact size and readability.

In many games, roll results are used to resolve actions by comparing the d20 result, plus any modifiers, against a target number such as a difficulty class or an attack AC. A higher roll increases the likelihood of success, with 20 often treated as a critical success and 1 as a failure, though specific rules vary by system. The d20 became especially central to the Dungeons & Dragons system beginning with the third edition, and the broader d20 System has been used by many other role-playing games.

Manufacture and form vary. Most d20s are injection-molded plastic or resin, with engraved or painted numerals. Higher-end examples may be metal, wood, or gemstone, and some dice feature color-coded or stylized typography with special artwork. The 20 face is commonly highlighted or colored to aid quick recognition; some sets are designed to be symmetrical for balance. While most modern d20s follow the opposite-face-sums-to-21 convention, some novelty dice do not.

Outside core RPG use, the term d20 is widely understood as shorthand for the twenty-sided die, and the die is used in various games and educational settings to teach probability and statistics.