How to roll a d100

Percentile dice


Sometimes a game tells you to use a "percentile dice" or a d100. That can be confusing if you're not used to it, so here's how it's done.

Novelty die notwithstanding, there's no such thing as a d100. Instead, you use any one of four methods:

  • Two ten-sided dice (d10) rolled in succession
  • Two different colours of ten-sided dice (d10) rolled together
  • A percentile die and a d10
  • Any other way you know to get a random number between 0 and 99

Two ten-sided dice

You've gone out and bought exactly one dice set, and so you've got exactly one ten-sided die.

  1. Roll your d10 once. This is the tens place.
  2. Roll your d10 again. This is the ones place.
  3. Picture the two numbers you just rolled, side by side, to form a single digit.

For example, suppose you rolled an 8 and then a 2. You've rolled 82.

If you rolled a 1 and then a 9, then you've rolled 19.

If you rolled a 0 and a 1, then you've rolled a 1.

Here's the weird one: When you roll a 0 and a 0, you have rolled a 100.

Two d10s in different colours

If you've got two d10s, each a different colour, then you can use one as the tens die and the other as the ones die. Declare which is which before you roll. Personally, I have a green die that serves as my tens die, and a black die for ones.

  1. Roll both dice.
  2. Assemble a number from your roll result, based on which colour represents tens and ones.

For example, suppose you roll a 7 and 5. You've rolled 75.

If you roll a 0 and 2, then you've rolled 2.

If you roll a 1 and 0, then you've rolled 10.

Here's the weird one: When you roll a 0 and a 0, you have rolled a 100.

A percentile die and a d10

You can buy a special "percentile" die from your friendly local game store. Instead of single digits, it's got double digits on it. It's a lot like using a different colour die as your tens die, except instead of a different colour it's just got more numbers on it.

  1. Roll both dice.
  2. Combine the percentile die with the d10 result.

For example, suppose you roll a 30 and a 3. You've rolled 33.

If you roll a 00 and then a 3, then you've rolled 3.

If you roll a 10 and a 0, then you've rolled 10. That's tricky, because it looks like 100, but it's not. It's one ten with zero one added on.

So how do you get 100? When you roll a 00 and a 0, you have rolled a 100.

If it helps, consider that the only time it's possible to get 100% of anything on percentile dice is when all digits are "0". When you roll three 0s, you have the only 100% possible, at least visually, on those dice.

High and low

Whether a roll of the highest value (000) is good, or whether you actually want a low roll (001) depends entirely on the game you're playing. Games like Call of Cthulhu and Stalking the Night Fantastic reward low rolls (because you're aiming for a number within your range of skill), while other games reward high results because they represent a high likelihood of something occuring.

Regardless of the implications, though, you now know how to roll a d100.

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