Free · No sign-up · Cryptographically random, fairness-tested
Roll virtual dice for tabletop RPGs, board games, or any random selection. Supports all standard polyhedral dice: d4, d6, d8, d10, d12, d20, and custom.
Fair question to ask of any online dice roller, and an easy one to dodge. So here are the numbers.
This roller uses crypto.getRandomValues() — the same random source browsers use for encryption keys — rather than the ordinary Math.random(). That is more than dice strictly need, but it costs nothing.
A d20 test over 200,000 rolls gave 18.51 on 19 degrees of freedom, against a threshold of 30.14. Both pass comfortably. Every face turned up within a quarter of a per cent of where it should.
A physical die, by contrast, is only as fair as its manufacture. Cheap injection-moulded dice have air bubbles, uneven pips and rounded corners that wear unevenly. Casino dice are made to tight tolerances with flush-filled pips for exactly this reason — and they get retired regularly.
Every tabletop game uses the same shorthand, and it takes about ten seconds to learn.
| Notation | Means | Range |
|---|---|---|
| 1d20 | One twenty-sided die | 1–20 |
| 2d6 | Two six-sided dice added together | 2–12 |
| 3d6+2 | Three d6, plus two | 5–20 |
| 1d8-1 | One d8, minus one | 0–7 |
| 4d6 drop lowest | Roll four, discard the worst | 3–18 |
| d100 | Percentile — usually two d10s | 1–100 |
The calculator above handles all of these: pick a die, set how many, add a modifier, and tick drop-lowest if you need it.
| Die | Shape | Average roll | Typically used for |
|---|---|---|---|
| d4 | Tetrahedron | 2.5 | Damage from daggers and darts |
| d6 | Cube | 3.5 | Almost every board game ever made |
| d8 | Octahedron | 4.5 | Longswords, and many RPG damage rolls |
| d10 | Pentagonal trapezohedron | 5.5 | Percentile rolls, damage |
| d12 | Dodecahedron | 6.5 | Greataxes — the least-used die in most RPG sets |
| d20 | Icosahedron | 10.5 | The one that decides everything in D&D |
| d100 | Two d10s | 50.5 | Percentage chances |
This is the most useful thing on the page for anyone playing board games. One die is flat — every face equally likely. Two dice are not.
| Total | Ways | Chance | |
|---|---|---|---|
| 2 | 1/36 | 2.78% | █ |
| 3 | 2/36 | 5.56% | ██ |
| 4 | 3/36 | 8.33% | ███ |
| 5 | 4/36 | 11.11% | ████ |
| 6 | 5/36 | 13.89% | █████ |
| 7 | 6/36 | 16.67% | ██████ |
| 8 | 5/36 | 13.89% | █████ |
| 9 | 4/36 | 11.11% | ████ |
| 10 | 3/36 | 8.33% | ███ |
| 11 | 2/36 | 5.56% | ██ |
| 12 | 1/36 | 2.78% | █ |
There is only one way to roll a 2 — snake eyes — but six ways to roll a 7. That makes 7 six times more likely than 2 or 12, and it is why the middle of the board is where the action is.
| Game | What the curve does |
|---|---|
| Monopoly | Properties seven squares past Jail are landed on far more than the corners |
| Catan | Hexes numbered 6 and 8 are the good ones; 2 and 12 barely produce anything |
| Craps | The entire game is built around 7 being the most common result |
| Backgammon | Doubles are rare, which is why hitting one matters so much |
The numbers that come up most often at a table, worked out rather than guessed.
| Question | Chance | Working |
|---|---|---|
| A 6 on one d6 | 16.67% | 1 in 6 |
| A natural 20 on a d20 | 5% | 1 in 20 |
| A natural 1 on a d20 | 5% | Exactly as likely as a 20 |
| Snake eyes — a 2 on 2d6 | 2.78% | 1 of 36 combinations |
| A 7 on 2d6 | 16.67% | 6 of 36 — the most common total |
| Doubles on 2d6 | 16.67% | 6 of 36 |
| At least one 6 on 2d6 | 30.56% | 11 of 36 — not 33% |
| Rolling 15 or higher on a d20 | 30% | 6 of 20 |
| Two natural 20s in a row | 0.25% | 1 in 400 |
| An 18 from 4d6 drop lowest | 1.62% | 21 of 1,296 combinations |
The classic method for rolling D&D ability scores, and a nice demonstration of how a small rule change shifts the odds.
| 3d6 | 4d6 drop lowest | |
|---|---|---|
| Average result | 10.50 | 12.24 |
| Chance of an 18 | 0.46% | 1.62% |
| Chance of 15 or more | 9.3% | 23.1% |
| Possible range | 3–18 | 3–18 |
Same range, noticeably kinder distribution. Discarding the worst die of four raises the average by almost two points and more than doubles your chance of a high score — which is exactly why the method exists.
Dice are one of the better teaching tools in mathematics, and a virtual roller removes the practical obstacles — nothing falls on the floor, and 500 rolls take a moment rather than an afternoon.
Dice are among the oldest game objects humans have. Long before cubes, people threw knucklebones — the ankle bones of sheep and goats, which land on four distinguishable faces and are found at archaeological sites across the ancient world.
| Period | Development |
|---|---|
| Ancient | Knucklebones used for games and divination across Mesopotamia, Greece and Rome |
| Early cubic dice | Six-sided dice appear in the Middle East and Asia, some remarkably close to modern shapes |
| Roman era | Dice games widespread and frequently regulated — loaded dice have been recovered from Roman sites |
| 1974 | Dungeons & Dragons popularises the full polyhedral set, taking the d20 mainstream |
| Today | Physical and virtual dice side by side, with online play making rollers standard equipment |
The pip arrangement has been stable for a very long time too: opposite faces on a standard d6 always add to seven, so 1 faces 6, 2 faces 5, and 3 faces 4. Pick up any die and check.
Is this dice roller fair?
Yes, and it has been tested. It uses crypto.getRandomValues(), the browser's cryptographic random source. Over 600,000 d6 rolls the chi-square statistic was 2.03 against a threshold of 11.07, and a d20 test over 200,000 rolls gave 18.51 against a threshold of 30.14. Both are comfortably consistent with fair dice.
How does an online dice roller work?
It asks the browser for a cryptographically random number and maps it onto the faces of the die. The whole calculation happens on your device — nothing is sent to a server, and the page works with the internet disconnected once it has loaded.
Can I roll multiple dice at once?
Yes. Set the number of dice and each is rolled independently, with the individual results and the total both shown. You can add a modifier and optionally drop the lowest die, which covers standard tabletop notation such as 3d6+2 or 4d6 drop lowest.
What is a d20?
A twenty-sided die — an icosahedron — best known from Dungeons & Dragons, where it decides most actions. Every face is equally likely at 5%, so a natural 20 and a natural 1 are equally rare. Its average roll is 10.5.
Why is 7 the most common roll on two dice?
Because there are more ways to make it. Six of the 36 possible combinations add to seven, while only one makes a two and one makes a twelve. That is a 16.67% chance of a seven against 2.78% for either extreme — six times more likely — and it shapes the design of Monopoly, Catan, craps and backgammon.
How many sides can a die have?
Physically, the common set runs d4, d6, d8, d10, d12, d20 and d100, though novelty dice with far more faces exist. This roller accepts custom dice up to 1,000 sides, which covers any practical need and a good deal of impractical ones.
Is a virtual die better than a real one?
For fairness, usually yes — a virtual die has no air bubbles, uneven pips or worn corners. Cheap physical dice can be measurably biased. Casino dice are manufactured to tight tolerances and retired regularly for exactly this reason. Real dice do, of course, feel considerably better to throw.
What does 4d6 drop lowest mean?
Roll four six-sided dice, discard the lowest, and add the remaining three. It is the traditional method for generating D&D ability scores. The range is still 3 to 18, but the average rises from 10.5 to 12.24 and the chance of scoring 15 or more more than doubles, from 9.3% to 23.1%.
Is a die "due" for a number after a losing streak?
No — that is the gambler's fallacy. Dice have no memory of previous rolls. After ten sixes in a row, the chance of another six is still exactly one in six. Streaks look meaningful but are simply what randomness produces over enough rolls.
Can teachers use this in class?
Yes, and it works well for it. It is free, needs no account, and hundreds of rolls take seconds — which makes demonstrating the law of large numbers practical in a single lesson. It is also useful for comparing theoretical against experimental probability, and for picking students or groups at random.
What is d100 and do I need a special die?
A d100 gives a number from 1 to 100, normally rolled with two d10s — one read as tens, one as units. Genuine hundred-sided dice exist but roll almost like marbles and take a while to settle. This roller does it in one step.
Do the rolls get saved anywhere?
Only in the roll history shown on the page, which keeps your last fifteen rolls and disappears when you close the tab. Nothing is transmitted to a server or stored between visits.
A dice roller is a simple thing that only has to do one job properly, and the way to know whether it does is to test it rather than assert it. The numbers at the top of this page are that test.
Whether you are playing a campaign, teaching probability, or just lost the dice from a board game some years ago, it will do the job — and unlike the originals, it will not roll under the sofa.
If you need a random number that is not a die face, the random number generator handles any range, and the probability calculator works out odds for events beyond the table above.
For something rather less rigorous, the love calculator is next door and makes no claim to accuracy whatsoever.