D20 Dice Roller Calculator

Roll a D20 die for your D&D or tabletop game sessions. Enter the number of dice, an optional modifier, and choose your roll type (normal, advantage, or disadvantage). Get back your individual roll results, total sum, and a roll distribution chart showing how your results spread across the 1–20 range.

How many D20 dice to roll at once

Add or subtract a flat modifier to the total (e.g. +3 from Strength)

Advantage and disadvantage apply only when rolling a single D20

Repeat the entire dice roll this many times

Optional label for your roll — does not affect the result

Results

Total Result (with Modifier)

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Dice Sum (before Modifier)

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Highest Single Die

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Lowest Single Die

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Critical Hit (natural 20)?

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Critical Fail (natural 1)?

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Individual Dice Roll Results

Results Table

Frequently Asked Questions

What is a D20 and why is it used in D&D?

A D20 is a 20-sided die, the most iconic die in Dungeons & Dragons and many other tabletop RPGs. It is used for attack rolls, skill checks, saving throws, ability checks, and initiative. The result determines success or failure based on the Difficulty Class (DC) or opponent's Armor Class (AC).

What does rolling with Advantage or Disadvantage mean?

When rolling with Advantage, you roll two D20 dice and take the higher result. Disadvantage is the opposite — roll two D20s and take the lower result. These mechanics apply only to single D20 rolls and represent favorable or unfavorable circumstances in D&D 5th Edition.

What is a Critical Hit (natural 20)?

A natural 20 means the die itself landed on 20 before any modifiers are added. In D&D, this is a Critical Hit on an attack roll, automatically succeeding and typically doubling the damage dice. It also means automatic success on most ability checks and saving throws.

What is a Critical Fail (natural 1)?

A natural 1 is when the die lands on 1 before modifiers. On an attack roll in D&D, this is an automatic miss regardless of bonuses. Some game masters also apply narrative consequences to a natural 1 on skill checks, though rules vary by table.

How random is this D20 roller?

This calculator uses JavaScript's Math.random() function, which generates pseudo-random numbers. While not cryptographically random, it is statistically equivalent to rolling a fair physical die for tabletop gaming purposes. Each face of the D20 has an equal 1-in-20 (5%) chance of appearing.

What is the probability of rolling a specific number on a D20?

Each face on a D20 has exactly a 1/20 or 5% probability. The chance of rolling a natural 20 (critical hit) is 5%, and so is the chance of rolling a natural 1 (critical fail). When rolling with advantage, the probability of getting a 20 rises to about 9.75%, and with disadvantage it drops to approximately 0.25%.

Can I roll multiple D20 dice at once?

Yes — set the Number of Dice field to any value between 1 and 20. The calculator rolls each die independently and displays individual results, the sum, the highest roll, the lowest roll, and the total with your modifier applied.

What is the average result of a D20 roll?

The average (expected value) of a single D20 roll is 10.5, since results range uniformly from 1 to 20. Adding a modifier shifts the average accordingly — for example, with a +3 modifier the average becomes 13.5. Rolling with advantage raises the average to approximately 13.8, while disadvantage lowers it to about 7.2.

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