A D20 is a 20-sided die (icosahedron) — the iconic die of Dungeons and Dragons. Each face shows a number from 1 to 20. It is used for attack rolls, saving throws, and skill checks in D&D and many other tabletop RPGs. A natural 20 (rolling the maximum) is called a 'critical hit' and a natural 1 is a 'critical failure'.

What does 2d6 mean in dice notation?

Dice notation uses the format XdY where X is the number of dice and Y is the number of sides. 2d6 means roll 2 six-sided dice and sum the results (possible totals: 2–12). 4d6 means roll 4 six-sided dice. Modifiers like 2d6+3 add a fixed number to the result. Drop-lowest notation like 4d6kh3 means roll 4d6 and keep the highest 3 — commonly used for D&D character attribute generation.

What types of dice are used in Dungeons and Dragons?

Standard D&D uses seven dice types: D4 (tetrahedron, 4 sides), D6 (cube, 6 sides), D8 (octahedron, 8 sides), D10 (pentagonal trapezohedron, 10 sides, numbered 0–9 or 1–10), D12 (dodecahedron, 12 sides), D20 (icosahedron, 20 sides), and D100 (percentile, two D10s or a special die). Our virtual dice roller supports all of these.

Are virtual dice truly random?

Virtual dice use pseudorandom number generators (PRNGs), specifically cryptographically secure PRNGs in modern browsers via the Web Crypto API (Math.random() uses this under the hood). While not truly random in a quantum physics sense, they are statistically indistinguishable from true randomness for gaming purposes. Each die face has an exactly equal probability of appearing, which is actually fairer than most mass-produced physical dice.

What is the average roll for each die type?

Average rolls (expected value = (sides + 1) / 2): D4 = 2.5; D6 = 3.5; D8 = 4.5; D10 = 5.5; D12 = 6.5; D20 = 10.5; D100 = 50.5. For multiple dice, multiply the single-die average by the number of dice. 3d6 averages 10.5; 2d6 averages 7. Adding a modifier shifts the average: 2d6+3 averages 10.

What is a critical hit in D&D?

A critical hit (or 'nat 20') occurs when you roll a natural 20 on a D20 attack roll. This means the attack automatically hits regardless of the target's armor class, and the damage dice are doubled. Some game systems also trigger critical failures on a natural 1 — an automatic miss regardless of bonuses. Critical hits are exciting moments that can dramatically shift combat outcomes.

How do I roll dice for D&D character stats?

The most common method is 4d6 drop lowest: roll 4 six-sided dice, drop the lowest die, sum the remaining three. Repeat 6 times for each ability score (Strength, Dexterity, Constitution, Intelligence, Wisdom, Charisma). This gives scores ranging from 3–18, averaging around 12-13. Use our dice notation field: type '4d6' and roll 6 times, dropping the lowest each time.

What is the probability of rolling a specific number on a die?

Each face of a fair die has an equal probability of 1/sides. On a D6: probability of any specific number = 1/6 ≈ 16.67%. On a D20: 1/20 = 5%. On a D100: 1/100 = 1%. For multiple dice: probability that 2d6 sums to 7 = 6/36 ≈ 16.67% (it's the most likely sum — six combinations reach 7). Probability that 2d6 both show 6 = (1/6)² = 1/36 ≈ 2.78%.

Can I use a keyboard shortcut to roll dice?

Yes! On our Dice Roller, press the Spacebar to roll your selected dice instantly without clicking. This makes rapid repeated rolling much faster during gameplay. You can also press Enter in the dice notation field to roll with DnD notation like '2d6+3'.

What is a D100 percentile die used for?

A D100 (percentile die) generates a random number from 1 to 100. It is used for random tables, percentage-based skill checks, wild magic surges, random loot tables, and encounter tables in tabletop RPGs. Physically, it is either a special spherical 100-faced die (Zocchihedron) or two D10s — one for tens digit (00, 10, 20...90) and one for units digit (0-9), where 00+0 = 100.

D4 · D6 · D8 · D10 · D12 · D20 · D100

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Dice Types

All 7 RPG Dice Explained

Every die used in Dungeons and Dragons, Pathfinder, and other tabletop RPGs.

▲ D4 — Tetrahedron

4-sided pyramid. Reads from the base edge, not a point. Range: 1–4. Used for: small weapon damage (dagger, sling), spell dice (some spells), feature bonuses. Average: 2.5.

⬜ D6 — Cube

The standard 6-sided die used in most board games. Range: 1–6. Used for: short sword, rapier, many spell dice (fireball = 8d6), stats in some systems. Average: 3.5.

⟐ D8 — Octahedron

8-sided diamond shape. Range: 1–8. Used for: longsword, rapier (versatile), warlock Eldritch Blast, cleric healing spells. Cleric hit die. Average: 4.5.

⬠ D10 — Pentagonal Trapezohedron

10-sided. Range: 1–10 (or 0–9). Two D10s make a D100. Used for: rapier, pike, heavy crossbow, fighter/paladin hit die. Average: 5.5.

⬡ D12 — Dodecahedron

12-sided. Range: 1–12. The Barbarian's hit die. Used for: greataxe damage, some high-damage features. Least commonly needed die. Average: 6.5.

⬟ D20 — Icosahedron

THE die of D&D. Range: 1–20. Used for: all attack rolls, saving throws, ability checks, death saving throws. Natural 20 = critical hit. Natural 1 = critical failure. Average: 10.5.

Probability Reference

Dice Statistics & Probability

Expected values, ranges, and probability of rolling maximum for each die type.

Die	Average	Min	Max	P(Max)	P(≥ Half)	Common Uses
D4	2.5	1	4	25.0%	50%	Dagger, small spells
D6	3.5	1	6	16.7%	50%	Short sword, fireball dice
D8	4.5	1	8	12.5%	50%	Longsword, healing spells
D10	5.5	1	10	10.0%	50%	Heavy weapons, hit die
D12	6.5	1	12	8.3%	50%	Greataxe, Barbarian HD
D20	10.5	1	20	5.0%	50%	Attack rolls, saving throws
2D6	7.0	2	12	2.78%	58.3%	Greatsword, stat rolls
D100	50.5	1	100	1.0%	50%	Percentile checks, wild magic

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Rolling D&D Character Stats — The 4d6 Drop Lowest Method

The classic method: roll 4d6, drop the lowest die, sum the remaining three. Repeat six times for six ability scores. Expected average per score: ~12.24. This gives scores ranging from 3–18. Use our dice roller — set to D6, count = 4 — roll six times and drop the lowest each time. For standard array instead: 15, 14, 13, 12, 10, 8 (no rolling needed).

Dice Notation & Probability Formulas

Standard Dice Notation (XdY+M)

Format: [count]d[sides][+modifier] Examples: 1d6 = roll 1 six-sided die (range: 1–6) 2d6 = roll 2d6, sum results (range: 2–12) 4d6+3 = roll 4d6, sum, add 3 (range: 7–27) 1d20-1 = roll D20, subtract 1 (range: 0–19) 3d8 = roll 3 eight-sided dice (range: 3–24) Expected value (average): E(XdY+M) = X × (Y+1)/2 + M E(2d6) = 2 × 3.5 = 7 E(3d6) = 3 × 3.5 = 10.5 E(4d6+3) = 4 × 3.5 + 3 = 17 Range: Min = X + M Max = X×Y + M

Probability of a Specific Roll

P(single die = k) = 1/Y for any face k P(D6 = 4) = 1/6 ≈ 16.67% P(D20 = 20) = 1/20 = 5.00% (nat 20) P(D20 = 1) = 1/20 = 5.00% (nat 1) P(D20 ≥ 15) = 6/20 = 30% (DC 15 check, +0 mod) P(D20 ≥ 15, +5 bonus) = P(D20 ≥ 10) = 11/20 = 55% For 2d6, number of ways to make sum S: Sum 7 = 6 ways → P = 6/36 = 16.67% (most likely) Sum 2 = 1 way → P = 1/36 = 2.78% (snake eyes) Sum 12= 1 way → P = 1/36 = 2.78% (boxcars)

D&D Advantage and Disadvantage

Advantage: Roll 2d20, keep higher Average with advantage ≈ 13.83 (vs 10.5 normal) P(nat 20 with advantage) = 1 - (19/20)² = 9.75% Disadvantage: Roll 2d20, keep lower Average with disadvantage ≈ 7.18 P(nat 1 with disadvantage) = 1 - (19/20)² = 9.75% To simulate: roll D20 twice in our roller, take the higher (advantage) or lower (disadvantage)

Frequently Asked Questions

A D20 is a 20-sided die (icosahedron) — the iconic die of Dungeons and Dragons. Each face shows 1–20. Used for attack rolls, saving throws, and skill checks. Rolling a natural 20 = critical hit (automatic success + double damage). Natural 1 = critical failure. At +0 modifier, you have a 5% chance of rolling any specific number. Our D20 roller is available with one click on the D20 button above.

2d6 = roll 2 six-sided dice and sum (range 2–12, average 7). XdY+M format: X = number of dice, Y = sides, M = modifier. Examples: 4d6 (roll 4 six-sided dice), 1d8+4 (roll D8, add 4), 3d10-2. Use our Notation field above — type your expression and press Enter or click Roll. Supports positive and negative modifiers.

D&D uses 7 die types: D4 (dagger, small weapons), D6 (short sword, fireball), D8 (longsword, healing spells, cleric HD), D10 (heavy weapons, fighter HD), D12 (greataxe, barbarian HD), D20 (all rolls — the main die), D100 (percentile checks, wild magic surge). Our virtual roller supports all seven with one-click switching.

Virtual dice use pseudorandom number generators (PRNGs) — statistically indistinguishable from true randomness for gaming. Each face has exactly equal probability. This is actually fairer than physical dice, which can have manufacturing imperfections that bias certain faces. Our dice roller uses JavaScript's Math.random() which browsers implement with cryptographically-secure PRNGs.

Formula: Average = (sides + 1) / 2. D4 = 2.5; D6 = 3.5; D8 = 4.5; D10 = 5.5; D12 = 6.5; D20 = 10.5; D100 = 50.5. For multiple dice multiply by count: 3d6 = 10.5; 2d8 = 9. Add modifiers to the average: 2d6+3 = 10. Our statistics panel tracks your actual rolling average so you can see how it converges on the expected value over many rolls.

Rolling a natural 20 on a D20 attack roll = critical hit: automatic success and double the damage dice (not total). If a sword does 1d8+4 damage, a crit = 2d8+4 (not doubled modifier). Natural 1 = automatic miss. With Advantage (roll 2d20, keep higher), probability of a nat 20 jumps from 5% to 9.75%. Some class features lower the crit threshold (Paladin Improved Divine Smite, Champion Fighter).

Standard method: 4d6 drop lowest, repeat 6 times. Roll 4 six-sided dice, drop the lowest, sum the remaining 3. Gives scores between 3–18, averaging ~12.24. Use our roller: select D6, set count to 4, roll 6 times. Alternatives: Standard Array (15,14,13,12,10,8 — no rolling); Point Buy (each ability costs points from a budget); Straight 3d6 (3 six-sided dice, harsher); or 2d6+6 (more heroic, min 8).

P(specific face) = 1/sides. D6: 16.67% per face; D20: 5% per face; D100: 1% per face. For sums with multiple dice: P(2d6 = 7) = 6/36 = 16.67% (most likely). P(2d6 = 2 or 12) = 1/36 = 2.78% (least likely). D20 skill check: P(≥ DC 15 with +5 bonus) = P(D20 ≥ 10) = 55%. See our probability table above for all common die types.

Yes! Press Spacebar to roll your selected dice without clicking. Press Enter in the notation field to roll a custom XdY expression. These shortcuts make rapid repeated rolling much faster during gameplay. You can also quickly change die types with the type buttons and adjust count with the + / − buttons before pressing Space.

D100 (percentile die) generates 1–100. Used for: random encounter tables, wild magic surges, percentage skill checks, random loot tables. Physically: a spherical 100-faced die (Zocchihedron) or two D10s — one tens (00, 10, 20...90) + one units (0–9), where 00+0 = 100. In D&D 5e, Sorcerers rolling a wild magic surge must roll D100 on a 38-entry table. Each result has a 1% chance.

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