DICE / 4 MINUTE READ

Dice notation for people who just found a D20.

Tabletop games describe dice with a compact code. Once you know how to read it, “roll 2d8 + 3” becomes an instruction rather than an incantation.

What the letter D means

In dice notation, the number after the letter D tells you how many sides the die has. A D6 is the familiar cube with faces numbered one through six. A D20 has twenty faces. The standard polyhedral set also includes D4, D8, D10, and D12 dice.

A number before the D tells you how many dice to roll. “2d6” means roll two six-sided dice and add the results. If no number appears before the D, one die is implied.

Common examples

• 1d20: one twenty-sided die, often used for checks and attacks.
• 3d6: three six-sided dice, producing totals from 3 to 18.
• 2d8 + 4: two eight-sided dice, then add a modifier of four.
• 1d100: a percentile result from 1 to 100, often rolled with two D10s.

Ranges and averages

The minimum result of a group of dice is the number of dice. The maximum is the number of dice multiplied by the number of sides. Two D6 dice therefore produce totals from 2 to 12. The average of one die is (sides + 1) / 2, so a D6 averages 3.5 and a D20 averages 10.5.

Multiple dice create a curve rather than a flat distribution. With 2d6, seven is more likely than two because several combinations total seven, while only snake eyes totals two.

Advantage and disadvantage

Some role-playing systems ask players to roll two D20s and keep the higher result for advantage or the lower result for disadvantage. This changes the probability distribution without changing the possible minimum or maximum.

Choosing the right die

Use the die named by the rules of the game. For custom activities, larger dice create more possible outcomes, while several smaller dice produce totals concentrated near the middle. That difference is useful when designing games or classroom probability exercises.