A d20, or twenty-sided die, is a die that has an equal chance of rolling the integers from 1 to 20. The standard shape of a d20 is a regular icosahedron, in which form it appears in the standard 7-dice set used in role-playing games like Dungeons & Dragons.
A regular icosahedron is a polyhedron with 20 faces that are all equilateral triangles. It is the Platonic solid with the most faces. The standard form available for purchase has its faces numbered from 1 to 20, with opposite faces adding up to 21.
The standard form is not the earliest type of twenty-sided die used in the hobby (see below for earlier forms), and was developed around 1980 specifically for its use in Dungeons & Dragons by TSR and Creative Publications. They became widely accessible by being sold with the Tom Moldvay Dungeons & Dragons Basic Set from 1981.
Early twenty-sided diceEdit
Twenty-sided dice were in use by wargamers and hobbyists before the development of Dungeons & Dragons. For example, as early as 1963 they were used in naval wargaming situations by the US Naval War College, although these only had the numbers from 1 to 10 instead of 1 to 20, and were used in pairs as percentile dice.
Similar twenty-sided dice marked 0-9 were adopted in a limited capacity by hobby wargamers in the late 1960s and early 1970s. For example, an advertisement in a 1971 issue of Wargamer's Newsletter offered a pair of 20-sided dice for £0.42 (GBP) or $1.20 (USD), sold as percentage dice. They appear to be marked with 0-9 twice. These were the dice that Gary Gygax obtained and used as d20s, first in his World War 2-era game Tractics, and later in D&D. He recommended that one of the sets of numbers from 0-9 be coloured in so that it was easier to tell which were supposed to be numbers from 1-10, and which were supposed to be numbers from 11-20.
These dice continued to be used throughout the 1970s until they were replaced by the now-familiar standard form.
While Dungeons & Dragons uses every type of die in the standard set, the d20 is the main die used for its random resolution mechanic. In fact, the d20 is used only for resolution and not for other types of rolls. Although the 3rd edition Player's Handbook in 2000 initially allowed the monk to deal 1d20 damage at high level, this was revised to 2d10 in the 2003 Player's Handbook v.3.5 to preserve the d20's special meaning.
The d20 is so widely recognized in its D&D resolution context that the D20 System (a generic system derived from Dungeons & Dragons 3rd edition in the year 2000) is named after it, and games derived from D&D or using a d20 resolution mechanic are commonly referred to as "d20 games" whether they use the D20 System or not. The more recent and wholly distinct 2d20 system by Modiphius is also named after the d20 die.
In Dungeons & Dragons, the d20 is used for core mechanics such as attack rolls, saving throws, ability checks and skill checks. Prior to D&D 3rd edition, roll-under checks were common, e.g. rolling a d20 and aiming to roll lower than your own Strength score. From 3rd edition onward, the d20 system established a core mechanic of rolling 1d20, adding relevant modifiers and bonuses, and aiming to meet or exceed a target number set by the Dungeon Master or game rules.
- ↑ 1.0 1.1 Jon Peterson (2020-02-22). "Identifying the Dice of the 1970s". Playing at the World. Retrieved 2020-03-08.
- ↑ Rob Doane (2019-10-26). "Historical Naval Wargaming Kit Demo (US Naval War College Museum)", 13m 0s. Invicta at YouTube. Retrieved 2020-03-08.
- ↑ Jon Peterson (2014-01-21). "A History of D&D In 12 Treasures", 7m46s. Jon Peterson at YouTube. Retrieved 2020-03-08.