Dnd Dice Roller Calculator - Roll D&D Dice with Notation, Advantage, and Modifiers

A Dnd dice roller is a virtual dice set for Dungeons & Dragons that takes a dice expression like 2d6+3, simulates each die as an independent uniform draw, sums the faces, applies any 5e mechanic such as advantage or Great Weapon Fighting, and reports the total alongside the individual faces. This Dnd dice roller handles the standard D&D dice sizes (d4, d6, d8, d10, d12, d20, d100), supports modifiers from -50 to 50, and runs single rolls or batches of up to 10000 rolls with the same seed.

• • Tabletop play at home or online: Roll attack, damage, and ability checks when the physical dice are missing.
• • D&D 5e rule reference: Confirm the mechanic for advantage, disadvantage, and Great Weapon Fighting reroll.
• • Probability homework and demos: Run 1000 or 10000 d20s to show the empirical mean converge to 10.5.
• • DM prep and encounter design: Estimate average damage from creature attacks like 2d8+4 or 3d6+2.

Each roll uses a seeded mulberry32 generator when a seed is provided, and Math.random() otherwise, so the same seed reproduces the same sequence on every load.

For the most common tabletop case of rolling exactly two six-sided dice, the 2 Dice Roller Calculator shows sums, doubles, and a Monte Carlo frequency table.

Each die is a discrete uniform random variable on the integers 1 through M. The roller draws N independent faces, sums them, optionally applies advantage, disadvantage, or Great Weapon Fighting reroll, then adds the modifier. With advantage or disadvantage on a single d20, two faces are drawn and the higher or lower is kept before the modifier is applied.

• N (dice count): Number of dice rolled at once. Integer from 1 to 100.
• M (die sides): Number of faces per die.
• K (modifier): Integer added to the rolled sum. Range -50 to 50.
• roll mode: Normal (default), advantage (2d20 keep highest), or disadvantage (2d20 keep lowest).
• great weapon fighting: On rerolls any 1 or 2 on a damage die once.
• batch size: Number of independent rolls to run in one click.

The expected value of a single NdM roll with no modifier is N times (M + 1) divided by 2, because each die has mean (M + 1) / 2 and expectation is linear. For a 2d6 attack damage roll that expected value is 7, for a 1d20 attack roll it is 10.5, and adding K shifts the mean to that target plus K.

Great Weapon Fighting rerolls any face of 1 or 2 on a damage die of size 12 or smaller once, matching the 5e SRD.

According to Wikipedia - Dice, Expected value of NdM is N times (M + 1) divided by 2

For arbitrary probability expressions built on top of these dice, the Probability Calculator accepts custom event formulas.

Four short definitions anchor the rest of the page. Keep them next to the roller so a beginner can refer back without leaving the page.

Independence is the assumption most often broken when these concepts are reused. Two rolls that share a die, a re-used seed, or a stop-after-streak rule all break independence, and the empirical mean of the batch will drift away from the theoretical value.

A d20 roll is the most general Bernoulli-like setup, and the Coin Flipper shows the same single-trial idea for heads or tails.

Set the dice expression, choose a 5e rule, then read the total plus the individual faces. The form recomputes on every input change.

1. 1 Pick a dice expression: Type the N into Dice Count and the M into Die Sides. For 2d6+3 that is 2 dice, 6 sides, and a +3 modifier.
2. 2 Enter the modifier: Use the ability modifier or attack bonus for the roll. A greatsword attack with +5 Strength is a 2d6 roll with a +5 modifier and Great Weapon Fighting on.
3. 3 Choose a 5e rule: Switch Roll Mode to advantage or disadvantage for a single d20 check. Switch Great Weapon Fighting to On only when the character has that fighting style and is rolling damage.
4. 4 Pick a batch size: Use 1 for a single roll, 1000 for a quick probability demo, or 10000 for a tight empirical mean. Larger batches run slower but report mean and crit counts more accurately.
5. 5 Optionally set a seed: Type any integer into the Seed field to reproduce the same batch later. The same seed always returns the same dice sequence.
6. 6 Read the results panel: Total, Dice Sum, Highest Die, Lowest Die, Natural 20 Count, Natural 1 Count, Batch Mean Total, and Latest Die Faces all update together.

For a level 5 greatsword attack with a +5 Strength modifier and Great Weapon Fighting on a hill dwarf fighter, set Dice Count to 2, Die Sides to 6, Modifier to 5, Roll Mode to normal, Great Weapon Fighting to On, Batch Size to 1, then read the Total and Latest Die Faces rows.

Once a single NdM roll is in hand, the Two Dice Probability Calculator returns the closed-form probability table for two-dice sums without running a batch.

The page combines a free-form dice expression, the two main 5e rules, and a batch runner in one form.

• • Any standard D&D expression: Dice Count 1 to 100 and Die Sides 2 to 100 cover d4, d6, d8, d10, d12, d20, and d100.
• • Built-in 5e rules: Advantage, disadvantage, and Great Weapon Fighting toggle in the same form.
• • Single rolls and probability batches: Batch Size 1 returns a single total; 1000+ reports the empirical mean and crit counts.
• • Transparent results: Highest Die, Lowest Die, and Latest Die Faces expose every individual face that went into the total.
• • Reproducible sequences: The optional Seed field turns the batch into a deterministic experiment.
• • Browser-only: No install and no login: open the page, type the expression, and roll.

A 1-roll run and a 1000-roll run use the same uniform face draw, so adding more rolls only changes the size of the output. Cross-checking the empirical mean against the theoretical NdM+K mean is the fastest way to spot a typo in N, M, or K, which is why the page exposes the batch mean alongside the latest total.

When the batch sequence needs streak analysis instead of a raw mean, the Coin Flip Streak Calculator takes a heads/tails sequence and returns run-length statistics.

The numbers are only as accurate as the assumptions behind each die. Five practical factors change what the rolled total really means at the table.

• • The page caps the batch at 10000 rolls to keep the browser responsive. Larger experiments should be split into multiple batches or run with a different tool.
• • Advantage and disadvantage only apply when N=1 and M=20. Other dice sizes and counts are run in normal mode even when the roll mode is set.
• • Great Weapon Fighting applies only to damage dice of size 12 or smaller. A d20 reroll would change the attack-roll mechanic, not the fighting style.

Real physical dice can show small biases in practice, especially worn or weighted sets. For security-sensitive draws, replace the roller with a true random source. Cross-check the batch mean against the theoretical value once per session.

According to D&D 5e System Reference Document (Wizards of the Coast), advantage and disadvantage are resolved by rolling 2d20 and keeping the higher or lower value, and the Great Weapon Fighting fighting style lets a character reroll a damage die of 1 or 2 once and use the new roll.

When a custom range of uniform draws is needed instead of a 1..M face, the Random Number Generator returns integers in a user-chosen interval.