What the Dice Roller does
This dice roller rolls any number of dice - d4, d6, d8, d10, d12, d20, d100 or a custom die with up to 1,000 sides - and shows each die, the total, the possible range and a history of your rolls. Pick the dice and press Roll, or type tabletop notation such as 3d6+2, 2d20kh1 for advantage or 4d6dl1 for character stats.
Each face comes from your browser's cryptographically secure random generator, converted to a die face by rejection sampling so that no number is even slightly more likely than another. Nothing is sent anywhere; the history lives only in this tab.
How to use it
- Choose the type of die and how many to roll. For a board game that is usually one or two d6; for role-playing games pick the die your rules ask for.
- Add a modifier if the rules add or subtract a fixed number, and choose advantage or disadvantage to roll two d20s and keep the higher or lower one.
- For anything more complicated, type dice notation instead: several groups (1d8+1d6+3), keep-highest (kh), keep-lowest (kl), drop-lowest (dl) or drop-highest (dh). Press Enter or Roll.
- Read the total, the individual dice (dropped dice are greyed out and shown in brackets) and the history table. Copy the result, download the history as CSV, or copy a link that opens the page with the same dice ready to roll.
Reading the results
The possible range is the lowest and highest total the dice can produce. The average roll is the long-run mean: (sides + 1) / 2 for each die, plus the modifier - 3.5 for a d6, 10.5 for a d20, 12.5 for 3d6+2. It is shown only where it is a simple formula; for keep and drop rolls it is left out rather than estimated.
Several dice do not make every total equally likely. With 2d6 there are 36 equally likely pairs, and six of them add up to 7, so 7 comes up one time in six while 2 and 12 come up one time in 36 each. A single die is the only case where every total is equally likely.
Streaks are normal. Rolling three 1s in a row on a d20 happens once in 8,000 tries; across a long session that is not a sign of a broken roller. The session statistics let you see the averages settle as the number of rolls grows.
Worked example: rolling with advantage
Advantage means rolling two d20s and keeping the higher, written 2d20kh1. Say the dice show 7 and 18: the roller keeps 18, greys out the 7, and the total is 18.
The chance of at least one 20 is 1 - (19/20)^2 = 9.75%, almost double the 5% of a single d20, and the average result rises from 10.5 to 13.825. Disadvantage (2d20kl1) mirrors it: the average falls to 7.175 and the chance of a 20 to 0.25%.
Formulas and scoring rules
- Fair face from a random number (rejection sampling)
limit = 2^32 - (2^32 mod sides); draw x until x < limit; face = (x mod sides) + 1A plain x mod sides would favour the lowest faces very slightly, because 2^32 is not a multiple of 6, 10 or 20. Rejecting the few values above the limit removes that bias completely; the tests prove it by feeding every possible value through the function.- Average of NdS+K
mean = N x (S + 1) / 2 + K- Advantage on a d20
P(result >= x) = 1 - ((x - 1) / 20)^2Disadvantage: P(result >= x) = ((21 - x) / 20)^2.
Dice notation in one minute
NdS means roll N dice with S sides: 3d6 is three six-sided dice, and d20 on its own means one. Add or subtract numbers and other groups with + and -. kh keeps the highest dice and kl the lowest (2d20kh1 is advantage, 2d20kl1 disadvantage), while dl and dh drop them (4d6dl1 rolls four and drops the lowest, the classic way to roll ability scores). d% is the same as d100. Up to 100 dice per group and 200 per roll.
Limitations: what the result does not prove
- It is a fair random roller, not a physical simulation: real dice can be slightly biased by manufacturing, and this is not.
- No roll is stored or sent anywhere. The history disappears when you close or reload the tab, so download the CSV if you need a record.
- Exploding dice, rerolls, success counting and fudge dice are not supported - use separate rolls for those mechanics.
- It should not decide money, gambling or anything where a dispute needs a verifiable record: there is nothing to prove afterwards which numbers were rolled.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- W3C Web Cryptography API - getRandomValues()
- MDN - Crypto: getRandomValues() method
- NIST SP 800-90A Rev. 1 - Random number generation using deterministic random bit generators
Frequently asked questions
How do I roll a dice online?
Choose the die, for example d6 for an ordinary six-sided die, set how many you want, and press Roll. Each die appears with its face, and the total is shown in large type with the range and the average beside it.
Is an online dice roller truly random?
This one uses crypto.getRandomValues, the browser's cryptographically secure generator, and converts its output to faces with rejection sampling so that every face has exactly the same probability. That is fairer than most physical dice, which are rarely perfectly balanced.
What does 3d6+2 mean?
Roll three six-sided dice, add them up, then add 2. The total can be anything from 5 to 20 and averages 12.5. Type it into the notation box exactly as written.
How does advantage and disadvantage work with a d20?
With advantage you roll two d20s and keep the higher; with disadvantage, the lower. It raises the average from 10.5 to 13.825, or lowers it to 7.175. Choose it from the Advantage list or type 2d20kh1 or 2d20kl1.
What is the most likely total with two dice?
Seven. Of the 36 equally likely ways two six-sided dice can land, six add up to 7, so it comes up one time in six on average. Totals of 2 and 12 each need one specific pair, a 1 in 36 chance.
How do I roll 4d6 and drop the lowest for character stats?
Type 4d6dl1, or press the "4d6 drop lowest" button. Four dice are rolled, the lowest is greyed out and shown in brackets, and the other three are added; repeat it six times for a full set of ability scores.
Can I roll a die with an unusual number of sides?
Yes. Choose Custom and enter any number of sides from 2 to 1,000, or type it in notation, such as 1d7 or 2d30. A d2 works as a coin toss, and d100 (or d%) gives a percentile roll.
Last reviewed by the A2Z.Tools team against the sources listed above.
