D&D Dice Explained: The Complete D20 System Guide

The Seven Standard Dice

A complete Dungeons & Dragons 5th Edition session uses seven types of dice, all part of the standard polyhedral set:

• D4 — Damage for small weapons (dagger, dart) and some spells (Cure Wounds at low levels)
• D6 — Damage for common weapons (shortsword, handaxe), rogue's Sneak Attack, and hit dice for sorcerers/wizards
• D8 — Damage for medium weapons (longsword one-handed, war pick), and hit dice for clerics/druids
• D10 — Damage for heavier weapons (heavy crossbow, halberd), and fighter/paladin hit dice
• D12 — Damage for the greataxe, barbarian hit dice
• D20 — Core resolution die for all checks, attacks, and saving throws
• D100 (two D10s) — Percentile rolls for Wild Magic surges, random tables

The D20 as the Core Resolution Die

Almost every uncertain outcome in D&D 5e resolves through a D20 roll. The system works like this: roll the D20, add relevant modifiers (ability score modifier, proficiency bonus, situational bonuses), and compare the total to a target number called the Difficulty Class (DC) or the opponent's Armor Class (AC).

If your total meets or beats the target, you succeed. If it falls short, you fail. The elegance of this single-die resolution system — as opposed to dice pool systems or probability tables — is that every roll is immediately interpretable: you can see the result, add your numbers, and know instantly whether you succeeded.

Attack Rolls

To attack a creature in melee or with a ranged weapon, roll 1D20 and add your attack bonus (ability modifier + proficiency bonus if you're proficient with the weapon). Compare the total to the target's Armor Class. A total that meets or beats the AC is a hit; below is a miss. On a hit, you then roll your weapon's damage die and add the appropriate modifier.

Common weapon damage dice: dagger 1D4, shortsword 1D6, longsword 1D8 (or 1D10 two-handed), greataxe 1D12, greatsword 2D6. The choice between a D8 and 2D6 for similar weapons has real mechanical implications — the D8 is uniform across 1-8, while 2D6 clusters around 7, making the greatsword more consistent and the greataxe more swingy.

Damage Dice and Spell Dice

Spells in D&D use every die type in the standard set. A Cure Wounds spell heals 1D8 + spellcasting modifier. A Fireball deals 8D6 fire damage. A Disintegrate deals 10D6+40 force damage. The wide range of spell dice creates different probability profiles — a D6 pool like Fireball is very consistent (averaging 28 damage), while a flat D8 heal has more variance relative to its size.

Critical hits, which occur on a natural 20 (the D20 landing on 20 before modifiers), double the number of damage dice rolled. A longsword normally deals 1D8; on a critical hit it deals 2D8. This rule makes high-damage weapons dramatically more explosive on critical hits — a greatsword's 2D6 becomes 4D6 on a crit, averaging 14 damage instead of 7.

Saving Throws

When a spell or effect targets you, you often roll a saving throw — a D20 + relevant ability modifier + proficiency bonus (if proficient in that saving throw type) against the spell caster's Spell Save DC. The six saving throw types correspond to the six ability scores: Strength, Dexterity, Constitution, Intelligence, Wisdom, and Charisma. Failing a saving throw typically means taking full effect; succeeding may halve damage or negate the effect entirely.

Skill Checks

Outside combat, the D20 resolves uncertain non-combat actions through skill checks. Trying to pick a lock? Roll Dexterity (Thieves' Tools), D20 + Dexterity modifier + proficiency bonus (if proficient). Persuading a noble? Roll Charisma (Persuasion) against a DC set by the Dungeon Master based on the difficulty of the task. Skill checks use the same D20 + modifier vs. DC structure as attacks and saving throws, creating a unified resolution system across all contexts.

Natural 20 and Natural 1

A natural 20 — rolling a 20 on the D20 itself before any modifiers — is an automatic hit on attack rolls and triggers a critical hit (double damage dice). On skill checks, it doesn't guarantee success by rules as written in 5e, but many Dungeon Masters house-rule exceptional success on natural 20s.

A natural 1 on an attack roll is an automatic miss, regardless of modifiers. On saving throws and skill checks, a natural 1 is merely a 1 (modifiers still apply) in standard rules — only attack rolls have the automatic failure rule by default. Natural 1s on attack rolls don't deal any damage and are often played for dramatic effect at the table.

Advantage & Disadvantage

When circumstances favor your success, you roll with advantage — roll two D20s and take the higher result. When circumstances work against you, you roll with disadvantage — roll two D20s and take the lower result. This elegant binary system replaces dozens of situational modifiers with a simple two-roll choice. For the full probability breakdown of advantage and disadvantage mechanics, see the Advantage & Disadvantage guide.

Initiative

At the start of combat, all participants roll initiative — a D20 + Dexterity modifier (and any initiative bonuses) — to determine turn order. Higher initiative goes first. Ties between player characters and monsters are broken at the Dungeon Master's discretion. Initiative is the only roll in a typical D&D session where everyone rolls simultaneously and the result is a ranking rather than a pass/fail.