Roll d100 (percentile) dice online with standard or two-d10 percentile mode. Includes success threshold checks, critical hits/fails, and decile distribution.
The d100, also called the percentile die, produces values from 1 to 100 with an even 1% chance for each result. Percentile RPG systems use that roll-under model so a skill score can act as a direct success chance.
This roller supports both a single-die d100 and the traditional two-d10 percentile method. You can set a success threshold, see pass or fail immediately, and track critical successes, critical failures, and decile distribution.
That makes it useful for percentile-based roleplaying, encounter tables, and any situation where you want a clean 1-to-100 random result.
Percentile systems are easier to use when the die result and the target number live in the same 1-to-100 scale. This roller keeps that relationship visible and makes it easier to see how often each decile appears across many rolls.
It is also useful for GMs who need a fast way to resolve repeated checks without doing manual pass-fail comparisons every time.
Each d100 produces uniform integer 1-100. P(success) = threshold/100. Expected value = 50.5. Variance = (100²−1)/12 = 833.25. Standard deviation ≈ 28.87.
Result: d100 → 42 ≤ 65 → Success
With a skill rating of 65%, rolling 42 is a success. There was a 65% chance of passing. A roll of 1-5 would be a critical success; 96-100 a critical failure.
Percentile (d100) systems have a unique elegance: your skill rating IS your success chance as a direct percentage. A character with 75% in a skill succeeds on any roll of 1-75. This transparency makes percentile systems intuitive for new players and easy to balance for designers.
The tradeoff is granularity. While a d20 system has only 5% increments, a d100 system can distinguish between a 62% and 63% success rate. This precision can feel like over-engineering for simple checks but shines in complex skill systems where incremental improvement matters.
The quintessential d100 RPG, Call of Cthulhu uses the percentile die for virtually everything. Character skills range from 01 to 99, and you roll against them constantly. The 7th Edition refined the system with three success tiers: Regular (≤ skill), Hard (≤ skill/2), and Extreme (≤ skill/5). This means a skill of 60 gives you 60% Regular, 30% Hard, and 12% Extreme success rates.
Fumbles occur on rolls of 96-100 when skill ≤ 49, or exactly 100 when skill ≥ 50. This asymmetry means skilled characters fumble less often — an elegant design touch.
The Zoccihedron, invented by Lou Zocchi in 1985, is a golf-ball-shaped 100-sided die. Due to its near-spherical shape, it takes forever to stop rolling and some faces are slightly more probable than others due to manufacturing imperfections. For this reason, most players prefer percentile dice (two d10s) or digital rollers for guaranteed fairness.
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A d100 is a single 100-sided die (Zocchihedron). Percentile dice use two d10s — one for tens (00-90) and one for units (0-9) — to generate the same 1-100 range. Both methods are equally fair.
Call of Cthulhu, RuneQuest, Warhammer Fantasy Roleplay, Rolemaster, Eclipse Phase, and many percentile-based systems. D&D uses d100 for random tables (wild magic surges, treasure).
Traditionally, 00 on the tens die + 0 on the units die = 100 (not 0). Some systems read it as 00, which is why we offer standard mode for clarity.
Varies by system. In Call of Cthulhu 7e, rolling ≤ skill/5 is an Extreme success, ≤ skill/2 is Hard, and exactly 01 is always special. Our tool flags ≤5 as critical.
Roll-under lets your skill rating directly show your success chance — a 65 in Combat means you succeed 65% of the time. This transparency is a key design feature of percentile systems.
Yes. Use multiple d100s when a system gives bonus or penalty dice. For roll-under systems, keeping the lowest result is usually the favorable option.