How to read percentile dice
Roll two d10s. One is marked 00, 10, 20 ... 90 and gives the tens; the other gives the units. Add them: 30 and 7 is 37. 00 and 0 together is 100, not zero. Some tables use two plain d10s and call one of them the tens die before rolling. The roller above draws both dice and adds them for you.
Where the d100 shows up
- Wild magic. A Wild Magic sorcerer who triggers a surge rolls on a d100 table, and the result can be anything from illusory butterflies and flower petals to a fireball centred on the sorcerer.
- Treasure. The magic item tables in the Dungeon Master's Guide are d100 tables.
- Anything with a percentage. "A 15% chance the bridge gives way" is a d100 roll of 15 or lower.
One number, two dice
Because each die is fair, every number from 1 to 100 comes up exactly one time in a hundred. That is the difference from rolling, say, 2d10 and adding them, which piles results up around 11.