Dice Mechanics: Randomness, Pools, Checks, and Tables

Dice mechanics are the rules and procedures that turn a die roll into a game result. A die supplies a random or uncertain input; the game decides when to roll, which dice to use, what to add or compare, and what the result means. The same physical d6 can therefore participate in very different mechanics.

Single checks and target numbers

A common mechanic asks a player to roll one die, add a modifier, and compare the total with a target number. In the D&D rules, a d20 is used for D20 Tests and modifiers can come from abilities, proficiency, circumstances, or other rules. This is a specific rules system’s procedure, not a universal definition of a d20.

When documenting a check, record the complete expression and comparison: the die, the number of dice, modifiers, target, and whether higher or lower is better. “Roll a d20” alone is not enough to explain the mechanic.

Damage and effect rolls

Many games use dice after an action succeeds to determine damage, quantity, duration, or another magnitude. The expression may use one die or several dice plus a modifier. The physical die type tells us the possible face values; the rule tells us how those values become an effect.

Dice pools and multiple rolls

A dice pool is a group rolled together. A system may count successes, keep the highest or lowest result, compare individual faces, total all dice, or spend a resource to reroll. These procedures produce different distributions even when the same dice are used. A DICEWIKI explanation should show at least one worked example and state what happens to unused dice.

Opposed rolls and random tables

In an opposed roll, two sides roll and the rules compare their results. The winner may be the higher total, the result with more successes, or the side that meets a stated threshold. In a random table, the roll selects a row or range. Percentile tables often divide 01–100 into ranges, so the table’s boundaries are part of the mechanic.

Special rules change the model

Advantage, disadvantage, rerolls, exploding dice, dropped dice, extra dice, and “keep the highest” procedures all change the probability model. A simple single-die formula should not be presented as if it explains those mechanics. When a rule is game-specific, cite the rulebook or official rules reference and keep the attribution visible.

How to document a dice mechanic

1. Identify the trigger: when does the player roll?
2. List the dice expression and any modifiers.
3. Explain how faces, symbols, or totals are interpreted.
4. State the comparison, target, success condition, or table range.
5. Show one example and name the rules source.

This method keeps a rules explanation reproducible and prevents a game convention from being mistaken for a physical property of the die.

Related DICEWIKI pages

Read dice notation, dice probability basics, and custom and specialty dice. Browse the games that use dice through the Dice Games directory.

Sources and editorial notes

1. D&D Beyond Basic Rules: Playing the Game, for D20 Tests, modifiers, damage rolls, random tables, and percentile examples.
2. Fate Core System Reference Document: Fate Dice, for an example of a symbol-based dice mechanic.
3. DICEWIKI editorial taxonomy, for separating physical dice data from rules procedures.