Aces Are Low: Rolling Percentile (d100) In D&D

Every so often, usually in an effort to troll the community, someone posts something like this article from Dice Dungeons, claiming that everyone is rolling percentile dice (d100s) wrong. This article shall stand as a firm and definitive rebuttal to these claims.


Every D&D player knows about the percentile dice. Percentile is the exception to every rule in the game, starting with the format of the roll. Rather than rolling one die, you roll two d10s (pentagonal trapezohedrons, for those who want to be especially pedantic), one as the tens and one as the ones. (Often, newer D&D sets include a d10 with two digits (10, 20, 30) to use for the tens die.) You then combine the results to find the total. For example, rolling 90 and 1 makes 91, while rolling 10 and 9 makes 19.

The Argument

Where some people go horribly, horribly wrong is when it comes to zeros. The way it is supposed to work is that zeros (0 and 00) are counted as zero, so that 10 and 0 is 10 and 00 and 0 is 100. The argument that occasionally rears its head takes the stance that this is somehow backwards, and that zeros should count as 10, meaning that 10 and 0 is 20 and 00 and 0 is 10 (under this weird paradigm, 100 would be 90 and 0).

Why They’re Wrong

Looking at this, one might think, “Alright, so while this offends me on a deeply spiritual level that I can’t ever hope to properly put into words, I do see that the system has its own consistent logic, even if it is ass-backwards and requires that you take the extra mental step of carrying the 1”. And maybe you would be right, but this is the Internet and we can’t just let such a trivial point go so easily, so we’re going to press on anyway with why this is inconvenient and problematic.

Problem 1: The Missing ‘1’

Let’s start with the argument of where the 1 comes in, because it’s central to the reason the zeros-are-ten camp (hereafter referred to as the Wrongs) provide for why their way is superior to the zeros-are-zero camp (hereafter referred to as the Rights).

The Wrongs insist that all rolls must fall within 1–100 (instead of 0–99 with zero counting as 100) because when you roll 00 and 0, there’s no 1 to go in front of the zeros, so therefore the result must be 10. Except… if there’s no 1, so where do they get 10? Why is adding it in to the smaller die superior to adding it to the bigger one? And why do you have to add it at all?

There are the same number of results between zero and 99 as there are between 1 and 100, so it all comes out in the wash. The Wrongs’ way of calculating the result just takes the more difficult option of carrying the 1 in an additional nine instances over the Rights. Just treat a roll of 0 as a result of 100 and call it a day!

Problem 2: Different Dice Meaning the Same Thing

Under the Wrong method, rolling 20 violates all reason by counting two different results as the same thing.

To roll 20 using the Wrong method, you have to roll a 1 (or 10 on a double-digit die) as the tens and a 0 on the ones to add 10. That’s two different numbers—1 and 0—both meaning the same thing, which is the kind of overly complicated nonsense only possible in the age of Common Core mathematics.

By contrast, the Right way has no duplications and no instances of different die results meaning the same thing. In other words, it makes mathematical sense.

Problem 3: The Right Way Is Literally In The Book

The Right way to roll percentile dice has been specifically laid out in the official books going back to the very first edition of the game. This is why 99.9% of the player base uses this method. In Fifth Edition, the specific instruction is included on page 6, and reads as follows:

Percentile dice, or d100, work a little differently. You generate a number between 1 and 100 by rolling two different ten-sided dice numbered from 0 to 9. One die (designated before you roll) gives the tens digit, and the other gives the ones digit. If you roll a 7 and a 1, for example, the number rolled is 71. Two 0s represent 100. Some ten-sided dice are numbered in tens (00, 10, 20, and so on), making it easier to distinguish the tens digit from the ones digit. In this case, a roll o f 70 and 1 is 71, and 00 and 0 is 100.

Now, granted, we at Dungeon Master’s Workshop have happily edited large sections of the official books and understand that some rules are just too convoluted or illogical to let stand, so we can’t rightly appeal to the authority of the text on its own. We do so in this case because the instruction is sensible and convenient, unlike the pedantic Wrong method, and provides clear direction that allows everyone to treat dice rolls consistently as opposed to arguing about the result. Dice are pretty fundamental to the game, so when in doubt, we should all be following what’s in the book.


The community has been rolling percentile the same way since the game was released more than 40 years ago. The current method works because people are clever enough to recognize it’s by far the easiest solution, requiring no additional mental power than just reading the numbers. Percentile rolling is already different from regular rolling, so all arguments against treating the zero differently are already invalid. There is consensus on this topic, and in a game with a bajillion other things that people already argue about, agreement on how to treat something as fundamental as dice is pretty important.

Given this importance of consistency, I recommend that everyone who reads this follows my lead in offering the following response to people who raise this matter in the future: “Every time someone doesn’t follow the PHB rules for percentile dice, Jeremy Crawford eats a kitten.”

Do you roll percentile the Wrong way? Then go away, we don’t want your comment below! 

2 thoughts on “Aces Are Low: Rolling Percentile (d100) In D&D”

  1. concise, and correct. I have seen some players/GMs try to claim that the method described within the books is “invalid”, citing that you just treat the d10 (non percentile version) as always, meaning its zero is actually 10, but the funny thing is that the percentile version of the d10 is STILL a d10, so you would have to treat it also as a d10 – which means they screwed up and now you are throwing 2 d10’s that are 1-10, and the first one is just multiplied by 10 to get the tens place, resulting in a range of 11 – 110, which is just absurd and foolish.

    We always know that there is never a such thing as a “zero roll” on ANY die, so we use this indisputable fact when rolling d100 using 2d10 with differentiated dice (typically now one shows with a trailing zero after each number – d10%). 00 + 1 through 90 + 9 will be easily and quickly seen for what they are, and 00 + 0 triggers the rule about “never zero roll” resulting in a 100 (integer wraparound for computer peeps).

    The Wrongs just need to give up on this failed idealistic crap about how to treat d10’s some convoluted and special way ONLY WHEN ROLLING 2 OF THEM and join the rest of the gaming race.

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