What is the largest die this can roll?

Up to 1000 sides, and up to 100 dice at once. Both are generous ceilings meant to stop a runaway number rather than a limit you are likely to hit in play.

Is a d3 or d7 actually fair here?

Yes. The generator draws a random number and corrects for any bias the conversion could introduce, so a 7-sided die is exactly as fair as a 6-sided one — something a physical die that shape usually cannot claim.

Custom Dice Roller

Not every game uses a standard six-sided die. Choose any number of sides from 2 to 1000, roll multiple dice at once, and add a flat modifier to the total.

Sides per die

Number of dice

Modifier

Added to the total

Seed (optional)

Replays the same sequence. Deterministic, not cryptographic.

Show the exact odds for each roll

Your roll will appear here, with the odds of getting it.

✓ The probabilities add up to one — 6 possible totals, from 1 to 6
✓ The average matches the closed form — 1 × (6 + 1) ÷ 2 is 3.5, computed independently of the distribution
✓ The spread matches the closed form — standard deviation 1.71, from each die's own variance of (s² − 1) ÷ 12
✓ The range is what the dice can reach — all ones is 1, all 6s is 6, and those are the first and last totals with any chance at all
✓ The distribution is symmetrical about the average — and level: every total from 1 to 6 is as likely as any other

What this generator does

Rolls dice with any number of sides you specify, rather than the standard polyhedral set, and keeps the session as you go — a session is rolls of one set of dice, and starts again when the sides, the count or the modifier change: the last twenty rolls, the running average against the average those dice should give, how often each face has appeared on dice of up to 20 sides, and the exact odds of each total unless the dice are too many to enumerate. Useful for board games with unusual dice, for teaching probability with a die that does not exist physically, and for any rule that calls for a size the shop does not sell.

How to use this tool

Set the number of sides per die.
Choose how many dice to roll.
Optionally add a positive or negative modifier.
Roll to see each result and the modified total.

Understanding the controls

Sides per die: Any whole number from 2 to 1000, so a d3 or a d100 are both possible. Every face is equally likely regardless of the number you choose.
Number of dice: From 1 to 100, rolled together. Each is rolled independently and shown separately as well as totalled.
Modifier: A flat number added to the total after the dice land. It moves the whole range of totals without changing the shape of the spread.
Seed: Empty for ordinary random rolls. Type anything to make the sequence repeatable — the same seed replays the same rolls in order. Deterministic, not cryptographic.
Show the exact odds: Puts the probability beside each roll: the chance of exactly that total and the chance of that total or better, both taken from the exact distribution rather than from a simulation; past 20,000 for dice times sides, or a million for dice squared times sides (100 dice stop at 100 sides), no odds and no session panel are shown.

Worked examples

A d3 for a quick three-way split: Set sides to 3, dice to 1. There is no physical three-sided die that rolls fairly by tumbling, so this is the practical way to get one.
Rolling 4d13 for a homebrew table: Set sides to 13, dice to 4, and read the total alongside each individual result — useful when a house rule cares about one die in particular as well as the sum.

Common use cases

Tabletop RPGs with non-standard dice
Custom probability games
Classroom maths and probability exercises

How this generator works

Each die is an independent draw of a whole number from 1 to however many sides you set, taken from your browser's Web Crypto random generator with the range conversion corrected so no face is favoured — a d13 is exactly as fair as a d6. Rolling several dice at once rolls each one separately and adds the modifier only once, after the sum, so the individual faces stay visible as well as the total.

Randomness and fairness

Every face is equally likely whatever number of sides you pick, because each die is drawn from your browser's cryptographic random source and values that would skew the range are discarded and redrawn. Give a seed and the source becomes a deterministic generator instead, repeating the same sequence for the same seed — reproducible rather than unpredictable, so it is for shared or repeatable sessions and not for anything that must not be guessable.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

Sides run from 2 to 1000 and dice from 1 to 100 per roll; a single d3-to-d1000 die is a genuine size no shop sells, but there is still a ceiling.
Every face is exactly as likely as every other, for any number of sides. It cannot reproduce a physical die's manufacturing quirks.
The session history lives in the page and clears when you close it.

Frequently asked questions

What is the largest die this can roll?: Up to 1000 sides, and up to 100 dice at once. Both are generous ceilings meant to stop a runaway number rather than a limit you are likely to hit in play.
Is a d3 or d7 actually fair here?: Yes. The generator draws a random number and corrects for any bias the conversion could introduce, so a 7-sided die is exactly as fair as a 6-sided one — something a physical die that shape usually cannot claim.