Roll percentile dice β a single number from 1 to 100, the format used for percentage chances in tabletop games and random tables. Add a modifier, roll several at once, and read the possible range alongside the result.
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Probability you can read directly
The appeal of percentile dice is that no translation is needed. If something has a 35% chance, you succeed on 35 or less. The number in the rulebook and the number on the dice are the same number, and a player can reason about their odds without doing arithmetic in their head.
This is a genuine design advantage over a d20, where a target number has to be converted before it means anything. “You need a 14” is opaque until you work out that it represents 35%. Systems built on percentiles put the probability directly in front of the player.
The two-dice convention
Physical percentile rolls use two ten-sided dice, one marked in tens. Roll a 30 and a 5 and you have 35. Roll two zeroes and you have 00, which nearly every system reads as 100.
The convention is fiddly in practice β arguments about which die was the tens are a familiar part of tabletop life β and it exists only because a hundred-sided die is impractical. A hundred-face solid is close enough to a sphere that it rolls for an unhelpfully long time.
A digital roll has no such constraint. Drawing once across the full range produces exactly the same distribution as the two-dice method, without the ambiguity.
Granularity and where it matters
The real difference between a d100 and a d20 is resolution. A d20 divides probability into twenty five-percent steps, so every outcome on a table occupies at least 5%. A d100 divides it into hundred one-percent steps, so a table entry can be genuinely rare β a 1% result is easy to express and impossible on a d20 without extra rolls.
That matters for treasure tables, wild magic effects, encounter tables and anything where the interesting entries should be uncommon. It matters much less for a straightforward success check, where five-percent granularity is finer than anyone can meaningfully feel.
The cost is reading time. Finding an entry on a hundred-row table is slower than on a twenty-row one, which is why many systems use both: a d20 for common rolls and a d100 where the detail earns its keep.
Modifiers on a flat distribution
Like a d20, a d100 is flat β every result equally likely β so a modifier changes the success chance by the same amount wherever you apply it. A +10 is worth exactly ten percentage points regardless of the target, which keeps the design honest and the arithmetic simple.
The one thing to watch is the range. A +10 on a d100 produces totals from 11 to 110, and whether results above 100 are possible or clamped is a rules question the dice cannot answer. The tool shows the achievable range so the situation is visible rather than assumed.
Independent rolls cluster
Rolling several percentile dice at once, it is entirely ordinary to see two results in the nineties or three under twenty. Each is drawn independently and knows nothing about the others. Clustering of this kind is what randomness genuinely looks like, and its absence would be the suspicious result.
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Building a percentile table
A d100 table assigns ranges of the hundred results to outcomes, and the widths encode the probabilities directly: an entry covering 01 to 40 happens 40% of the time.
The arithmetic is worth checking. Ranges must not overlap, and they must cover the whole hundred β a table that stops at 95 has a five per cent chance of producing nothing at all, which is the sort of gap that only surfaces mid-session.
Weighting is where percentile tables earn their place. Making one outcome twice as likely as another is just a matter of giving it twice the range, with no extra mechanics, which is why they are so common for treasure, encounters and wild effects.
How to use the D100 Dice Roller
- Choose how many percentile rolls you need.
- Add a modifier if your table or rule calls for one.
- Roll β the possible range is shown alongside the result.
Frequently asked questions
What is a d100?
A hundred-sided result, from 1 to 100. Physically it is usually rolled as two ten-sided dice, one giving the tens digit and one the units. Digitally it is a single draw across the full range, which produces exactly the same distribution.
Why do games use percentile dice?
Because the result reads directly as a percentage. A 35% chance succeeds on a roll of 35 or less, with no conversion step. That makes probabilities transparent to players in a way that "beat a 14 on a d20" does not.
How do two ten-sided dice make a hundred?
One die is designated the tens and one the units, giving 00 to 99. Most systems read 00 as 100. The tool skips the two-dice representation and draws directly, which avoids the argument about which die was which.
Is a d100 better than a d20 for random tables?
For fine-grained tables, yes β a d100 lets an entry occupy any whole percentage, so a 3% result is straightforward. A d20 forces everything into 5% steps. For quick tables the d20 is faster to read and perfectly adequate.
What does the modifier do?
It shifts the total up or down, which is how many systems represent circumstances that make something more or less likely. The tool shows the possible range including the modifier so it is clear what the roll can now produce.
Are all hundred outcomes equally likely?
Yes. Each is drawn with exactly a one in a hundred chance using rejection sampling, so there is no bias toward any part of the range.
Can I roll several at once?
Yes, and each is independent. Useful for resolving several percentage checks in one step, or for generating a batch of entries from a random table.
