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 known as the percentile die — generates numbers from 1 to 100, giving every outcome a clean 1% probability. It's the backbone of percentile-based RPG systems like Call of Cthulhu, RuneQuest, and Warhammer Fantasy Roleplay, where you roll under your skill rating to succeed.
Our d100 Dice Roller supports both standard single-die rolling (d100 = 1-100) and the traditional percentile method using two d10s (one for tens, one for units). Set a success threshold to instantly see pass/fail results, track critical successes and failures, and analyze your rolls across decile ranges.
Whether you're investigating eldritch horrors in 1920s Arkham or rolling on a random encounter table, this tool provides transparent, instant results with full statistical tracking. Check the example with realistic values before reporting. Use the steps shown to verify rounding and units. Cross-check this output using a known reference case. Use the example pattern when troubleshooting unexpected results.
Percentile systems require rolling d100 frequently, often multiple times per combat round. Our digital roller provides instant color-coded pass/fail results, eliminating the mental math of comparing rolls to skill values. The batch rolling feature lets GMs pre-roll skill checks for NPCs.
The decile distribution chart also helps players understand whether their session was lucky or unlucky — objectively comparing observed results against the expected flat distribution across all ten deciles.
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.
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! This is useful for systems with advantage or "bonus dice." Set 2d100 with keep-lowest for advantage (you want to roll under) or keep-highest for penalty.