Percentile Dice: How d100 and d% Rolls Work

Percentile dice are used to generate a result from 1 to 100. In the common tabletop convention, a d100 roll is made with two ten-sided dice: one die supplies the tens digit and the other supplies the ones digit. The two dice are often called percentile dice, or written as d%.

How a percentile roll works

Before rolling, designate which die represents tens and which represents ones. If the tens die shows 70 and the ones die shows 4, the result is 74. If both dice are numbered 0–9, a 7 and a 4 are read as 74. If both dice show zero, the usual convention is 100 rather than 0, provided the rules for the game use the standard d100 interpretation.

Some sets make the distinction easier by printing one die with 00, 10, 20, and so on. A 70 die together with a 4 die still gives 74. The marking helps the reader identify the digit position; it does not change the underlying two-die method.

What does 00 mean?

The answer depends on the rules that asked for the roll. In the common 1–100 convention, 00 paired with 0 means 100. A tens result of 00 paired with 7 means 7, usually written as 07 when a two-digit display is useful. A table may define its ranges as 01–05, 06–10, and so forth, so the table’s instructions take priority over a general convention.

This is why a DICEWIKI record should describe both the physical markings and the rules context. A ten-sided die marked 00, 10, 20, through 90 is a percentile die in many sets, but the exact reading still belongs to the rulebook or tool using it.

Probability in the fair-die model

If each face of each d10 is treated as equally likely and the dice are independent, the pair has 10 × 10 = 100 equally likely ordered outcomes. Each number from 1 to 100 therefore has one outcome in the basic model:

P(roll 37) = 1 ÷ 100 = 1%

For a range, count the included results. A table entry for 01–05 contains five outcomes, so its theoretical probability is 5 ÷ 100 = 5%. This is a mathematical model, not a test result proving that a particular physical pair is unbiased.

Percentile dice and a single d10

A normal d10 produces ten face values, not one hundred. A pair of d10s can encode a two-digit number because one die provides the tens position and one provides the ones position. This difference matters when a product listing says “d100”: check whether it means a single object with one hundred marked outcomes, a pair of percentile dice, or a virtual tool that implements the same range.

Some games use a single d10 for a 0–9 result and call for a separate multiplier or table. That is not automatically the same as a d100 roll. Record the actual rule expression rather than inferring it from the product’s appearance.

Common reading mistakes

• Reading 70 and 4 as 704 instead of 74.
• Changing the tens/ones assignment after seeing the roll.
• Treating 00 and 0 as zero when the table defines it as 100.
• Assuming every game uses the same 00 convention.
• Calling a theoretical 1% result a measurement of a physical die’s fairness.

How DICEWIKI records percentile dice

A useful record separates the physical object from the notation: number of dice, face markings, whether one die is numbered in tens, the stated result range, and the source rule or product description. When the source is unclear, the record should say so instead of silently choosing an interpretation.

For more context, see dice notation, standard dice types, and dice probability basics. You can also compare the explanation with the DICEWIKI probability tool.

Sources and editorial notes

1. D&D Beyond Basic Rules: Playing the Game, for the d100, percentile-dice, 00/0, and tens/ones conventions.
2. Wizards of the Coast D&D Essentials Rulebook, for an independent official example of percentile dice.
3. OpenStax, Probability, for the equally-likely-outcomes model used in the calculation.