How to Read a d100 Dice Roll. Are you doing it wrong?

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How to Read a d100 Dice Roll. Are you doing it wrong?


Welcome to the first installment of the GM’s Corner here at Dice Dungeons. This will be a section where we discuss GM things; from how to get over your anxiety as a first time GM to tips and tricks even pros can use.

This time, I have been specifically asked to talk about a subject that I am very passionate about, and have only seen discussed in one buried thread in some orphaned forum somewhere:

You are rolling your d100 rolls wrong.

Now, it’s probably not your fault; these things get passed on from GM to player, and then from player to other players… like some sort of transferable disease. Don’t understand what you’re doing wrong? Let me show you.

Ok, First off, I’m talking about rolling a percentile die along with a d10. If you’re rolling an actual d100, well, this discussion isn’t for you. Let’s look at our dice, shall we?

The d10 is a pretty common damage die used in various RPGs, ranging from a d20 system like Dungeons & Dragons to 2d6 systems like those using the Powered by the Apocalypse engine. Let’s go over what each side means when rolling it in this context, shall we?

Group of metal d10s

Now, let’s take a look at the percentile die. This has a very similar numbering scheme to the d10, with one very important distinction: there is an additional 0 after each number. These are used to denote the zeroes, tens, and nineties place.

metal percentile dice from dice dungeons

Now, you might be saying, “Uh, yea. Obviously. This is a dumb article written by a dumb-o”. Well, let’s just reserve that judgement until after this next bit, ok?

So, in order to get a d100 roll without using an enormous golf ball of a die, we roll a percentile die and a d10 and add the result, right?

For instance, this is 37.

37 on a d100 Dice Roll

And this is 82.

82 on a d100 Dice Roll

And this is 69. Nice.

69 on a d100 Dice Roll

But what, I ask you, would you call the following roll?

50 or a 60 on a d100 Dice Roll?

Every single person I know would call this roll a 50. You’re treating the 0 on the d10 as an actual 0. OK. So, then I ask of you, what is the following roll?

Is this a 7 on a d100 Dice Roll?

Well, that’s obviously a 7. You have 00 on the percentile, and a 7 on the d10. It can only be a 7. It sure as heck isn’t 107, right? Because that’s outside of the range of the d100 roll, right? Because a d100 roll is from 1-100, right?

Everything I’ve shown you so far is fine.

Or it would be, if it weren’t for one little thing…

You see, you cannot treat both the 0 on a d10 as a zero and the 00 on the percentile die as the ‘zero’s place marker’.

It works for the most part, sure. A 10 would be a 10 and 0 on the percentile and d10. Same works for 20, 30, etc…

But, dear friends, how do you roll a 100 this way?

Most people would say a 00 on the percentile and a 0 on the d10. BUT, given the facts I’ve just carefully laid out, that violates the rules you determine the rest of your rolls by. A 00-0 roll would, technically, be a straight up zero.

Instead of a 1-100 scale, you’ve made yourself a 0-99 scale.

 “Oh God, you’re right! How could we have been so stupid? How can we possibly repair this travesty?!” you cry out. Well, I’m benevolent enough a GM that I wouldn’t destroy your world view if I didn’t have a better one to replace it with. And, honestly, it’s pretty simple:


This way, everything works out perfectly. You can’t roll a zero; a 00-0 roll would be a 10. A 00-1 would be a 1. 90-0 is the coveted 100 roll. Sure, a 40-0 roll being a 50 isn’t immediately obvious, but this is the only internally consistent method I can see here.


Maybe you don’t want to change. That’s fine; change is hard. But know, fellow GMs and players, that the method you’re using is invalid. You’re changing the rules for different cases.

In a world where consistency in rules and mechanics is required, why too wouldn’t it be required when rolling the dice?


  • Long

    I think the range from 00-99 works just fine, just add +1 to your roll and it will turn the range from 1-100. Easy, no confusion. Just a little extra work, but no confusion wit the dice if 00-0 = 100 or 90-0 = 100, or w/e.

  • British Petroleum

    There is no wrong way to roll d100, but I prefer the 00-0 = 100/00-1= 1. There is no way to roll below a 1 and above a 100. it just makes more sense to me and it is the exception that proves the rule.

  • Eli

    I agree with the users saying:
    —D&D RAW couldn’t be clearer that 0-00 is meant to be 100 in that system.
    —treating 20-0 as 30, 50-0 as 60 etc. feels to me more unintuitive/inconsistent than having 0-00 be the only exception to an otherwise consistent pattern
    —Either method produces fair and unambiguous results as long as everyone at the table understands and agrees ahead of time which method will be used.

    I also just generally like the feeling of 0-00 being a special case result. It sort of reminds me of the green spaces on a roulette wheel or something.

  • Luke

    The system you’re proposing has room for confusion.

    Couldn’t you just add 1 to whatever score you roll, or subtract 1 from whatever table you’re referencing?

    You still have 100 possible scores in either case. You just need to shift the to roll match the 1-100 scale, or shift the table to match the 0-99 scale. The probabilities don’t change at all.

    Yeah, rolling a 50-5 and having it be 56 might feel a little off at first, but it’s a stupid-easy calculation and doing it for every roll feels more consistent and intuitive than adding 10, but only if you roll a zero on the d10 die. A 00-0 should make you feel like a loser and 90-9 should make you feel like a baller.

    Just my two cents.

  • Robert B

    It’s funny when I see comments about “00 & 0=100 is how it’s always been”. That’s the way it’s been since dnd picked it up, but percentile does in ttrpg predates dnd. The original method is 00=0 and 0=10. That’s from a very old game about the battle of Waterloo, where percentiles are the only dice used to determine outcomes of any action or event. Use whichever works best for your group is what I say, but this article depicts the original method.

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