Dice Roller
Left your dice bag at home? Roll 3d6+2, a d20 attack, or percentile dice right here — every die shown individually, modifiers applied to the total, and your last 10 rolls kept in view for the table to verify.
Die type
1–20
−20 to +20
Rolls use crypto.getRandomValues with rejection sampling, so each face is exactly equally likely — fairer than many physical dice, which can be biased by uneven edges or air bubbles. A d100 here is a single 1–100 roll, equivalent to rolling two d10s as percentile dice.
The Probability Behind the Rolls
One die is flat — every face equally likely — but sums of dice bunch in the middle. On 2d6 there are 36 possible outcomes and six of them total 7 (1+6 through 6+1), so 7 hits 6/36 ≈ 16.7% of the time, while 2 and 12 each show up just 1/36 ≈ 2.8%. Rolling with advantage (two d20s, keep the higher) lifts the average from 10.5 to exactly 13.825 — worth about +3.3 — because the higher of two rolls of k or less requires both dice to land at k or less.
Average roll by die
d4 2.5 d12 6.5 d6 3.5 d20 10.5 d8 4.5 d100 50.5 d10 5.5 NdX average = N × (X+1) ÷ 2 2d6: 7 is the most likely sum (6/36 ≈ 16.7%) d20 advantage: mean 10.5 → 13.825 (+3.3) 3d6+2: range 5–20, average 12.5
Frequently Asked Questions
What is the most likely roll on 2d6?
Seven — of the 36 equally likely outcomes, six combinations total 7 (1+6, 2+5, 3+4, 4+3, 5+2, 6+1), so it lands 6/36 ≈ 16.7% of the time. The extremes are rarest: 2 and 12 each have exactly one combination, 1/36 ≈ 2.8%. That triangle-shaped distribution is why 7 dominates games like craps and Settlers of Catan.
How much does advantage help on a d20?
Rolling two d20s and keeping the higher raises the average from 10.5 to exactly 13.825 — about +3.3, comparable to a sizable flat bonus. It helps mid-range targets most: the chance of rolling 10 or higher jumps from 55% to about 79.75%, while near-impossible rolls stay near impossible (a natural 20 only improves from 5% to 9.75%).
What does a notation like 3d6+2 mean?
Roll three six-sided dice, add them, then add 2: written NdX+M, it's the standard tabletop dice notation. 3d6+2 ranges from 5 to 20 with an average of 12.5 (each d6 averages 3.5, so 3 × 3.5 + 2). Set the die to d6, dice to 3, and modifier to +2 here to roll it.
Are online dice rolls fairer than physical dice?
Often, yes. This roller uses crypto.getRandomValues with rejection sampling, so each face has exactly equal probability. Physical dice can be measurably biased — uneven faces, air bubbles, or rounded edges shift frequencies, and cheap d20s have shown bias of several percent in tumbling tests. A casino-grade precision die is fair; the one from a board game box may not be.