Tabletop role-playing · probability notebook
Know what your dice are telling you
Worked probability for tabletop role-playing games: what a d20 roll under 40% really does, how 3d6 and 1d20 differ in shape, and how to build a character around the numbers instead of around hope.
Dice Maths
What a skill check really measures
A d20 roll under a fixed number is not a 40% chance of anything simple. Here is the arithmetic, with a working calculator and the cases where it breaks.
Walk the mainland note →Nearby islands
Why 3d6 feels steadier than a single d20
Same average, two different worlds: how summing dice squeezes the middle and trims the tails, with a full distribution table you can check by hand.
How to read 3d6+2 without guessing
The shorthand on a character sheet is a sentence about dice with three parts: how many, how many sides, and what you add. Read it once, correctly, and never misread a rule again.
Charted waters
Open the full index →The free rules offer three ways to get six ability scores: roll four dice and keep three, take a fixed array, or spend 27 points. Here is what each one produces, worked out exactly, with plain 3d6 as a baseline.