What Is a d100?
The hundred-sided die (d100) generates a number from 1 to 100, giving every result an equal 1% chance of appearing. In tabletop RPGs, a d100 roll is most commonly made using two ten-sided dice (called percentile dice) - one for the tens digit and one for the ones digit. A physical 100-sided die does exist (called a Zocchihedron), but percentile dice are far more practical and widely used.
The d100 is central to several major RPG systems and appears frequently in D&D for random tables, special abilities, and any situation where the game needs a precise percentage chance.
How Percentile Dice Work
To roll a d100 with physical dice, you roll two d10s together. One die (often a different colour or marked with tens: 00, 10, 20, etc.) represents the tens digit, while the other represents the ones digit. A roll of 40 and 7 gives you 47. A roll of 00 and 0 is read as 100.
This two-dice method is why percentile rolls are sometimes written as "d%" or "d100" interchangeably. QuickDice handles the maths for you - just select 100 sides and roll.
Where the d100 Appears in RPGs
- Wild Magic Surge (D&D) - When a Wild Magic sorcerer triggers a surge, the DM has them roll on a d100 table of 50 chaotic effects. Results range from harmless (you turn blue for 24 hours) to dramatic (you cast fireball centred on yourself). It is one of the most memorable d100 tables in the game.
- Random encounter and loot tables - D&D uses d100 rolls throughout the Dungeon Master's Guide and adventure modules to determine random encounters, treasure hoards, and trinkets. The 100-point scale allows designers to assign precise probabilities to rare and common outcomes.
- Call of Cthulhu - The entire skill system in Call of Cthulhu runs on d100 rolls. Players roll under their skill percentage to succeed, making the d100 the most-rolled die in the game. A Spot Hidden skill of 55 means you need to roll 55 or lower.
- Warhammer Fantasy Roleplay - Like Call of Cthulhu, WFRP uses a d100 "roll-under" system for skills and combat. The percentile scale makes it easy to understand your exact odds on any given check.
d100 vs d20: When to Use Each
The d20 divides outcomes into 5% increments, while the d100 works in 1% increments. This makes the d100 better suited for systems that want fine-grained probability control - a skill of 73% means exactly what it says. The d20, by contrast, works well for systems where modifiers and difficulty classes do the heavy lifting, with the die providing a broad random element.
Most modern D&D gameplay uses the d20 for core mechanics, reserving the d100 for tables and special effects where a wider range of outcomes is needed. Systems like Call of Cthulhu and Warhammer chose the d100 as their core mechanic specifically because players find percentage-based odds intuitive and easy to reason about.