Online Tool Store
Dice Roller
Roll up to 30 dice from d4 to d100 with an optional modifier, and keep every result with running averages. Runs entirely in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
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A first roll is shown above — change the settings and roll your own.
- Rolls
- 0
- Average
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- Lowest
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- Highest
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History
Newest first.
How it works
- Pick how many dice, which die type, and any modifier to add to the total.
- Press "Roll dice". Each die is shown individually, with the sum worked out underneath.
- Every roll is added to the history, and the average, lowest, and highest update as you go.
- Clear the history whenever you want a fresh set of statistics.
Why a naive roll is biased
The obvious way to turn a random byte into a die roll is to take the remainder:
face = (byte % sides) + 1 // subtly wrong
A byte holds 256 values, and 256 is not a multiple of 6. Values 0–251 spread evenly across the six faces, but the leftovers 252–255 land on faces 1–4 only. Those four faces therefore come up 43 times in every 256 bytes against 42 for faces 5 and 6 — about 2.4% more often. Small, but real, and it compounds over thousands of rolls.
This roller uses rejection sampling instead: it ignores any byte at or above the largest exact multiple of the die size and draws again.
limit = ⌊256 ÷ sides⌋ × sides // 252 for a d6, 200 for a d100
draw bytes until byte < limit, then face = (byte % sides) + 1
Every face then has exactly the same chance. For reference, the average of a fair d6 is 3.5, so 2d6 averages 7 — the running average above should settle near that figure the longer you roll.
FAQ
Are the rolls actually random?
Yes, and each face is equally likely. Rolls come from your browser's cryptographic random number generator, and the code discards and redraws the small uneven tail of the range rather than taking a shortcut that would quietly favour the low faces. See "Why a naive roll is biased" below for the detail.
Which dice can I roll?
d4, d6, d8, d10, d12, d20, and d100 — the standard tabletop set — up to 30 at a time, with a modifier from −100 to +100. The notation shown under the total, such as 2d6+3, is the usual shorthand for what you rolled.
How does the modifier work?
It is added once to the total, not to each die. Rolling 2d6+3 sums the two dice and then adds 3, so the range is 5 to 15. A negative modifier subtracts in the same way.
What do the average, lowest, and highest show?
They summarise the totals of every roll in your current session, including rolls made with different dice or modifiers. Clear the history to start a fresh set of statistics.
Is my roll history saved or sent anywhere?
Neither. The history lives only in this page while it is open — nothing is uploaded, and nothing is kept in your browser between visits. Reloading the page starts over.
Can I roll different dice together, like 1d20 and 2d6?
Not in a single roll — each roll uses one die type. Roll them one after the other and read the totals from the history, which keeps each roll listed with its notation.
How we compare
| Feature | Online Tool Store | Ad-supported dice sites | Real dice |
|---|---|---|---|
| Provably even faces, bias handled explicitly | ✓ | Usually fine, but the method is rarely stated | Close — cheap dice are measurably uneven |
| Running history, average, high and low | ✓ | Some show the last roll only | ✗ |
| No ads, no sign-up, nothing logged | ✓ | ✗ | ✓ |
| Rolls 30 dice at once without counting them out | ✓ | ✓ | Only if you own 30 dice |
| Mixed dice in one roll, e.g. 1d20 + 2d6 | ✗ | Better sites accept full dice notation | ✓ |
| Works with no power and no connection | Offline once loaded, but needs a device | ✗ | ✓ |
Handy when the dice are in the other room, when you need more than you own, or when a board game has lost its pieces — and the history means you can settle "what did you actually roll?" after the fact. For a full tabletop session with mixed dice in one throw, a dedicated notation roller still fits better.