Dice Dungeons d100 Metal Dice Sets

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

Welcome to GMs Corner. A new curated collection of opinion pieces from our local GMs.


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?

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This isn’t debatable. The rules are clear and in plan English:

“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 of 70 and 1 is 71, and 00 and 0 is 100.”


Padraic H

Ok, so, I get the logic of it, but the way most people are doing it doesn’t change the number of possible results and is easier math. Obviously, just as there is no 107 on the combo d100, there is also no 0. So, similarly to how the ace in blackjack can be the high or low, the 00 is as well, depending on what it’s coupled with. So:
etc etc until all that remains is the question of what to do with…
Which, since there is no 0 score, gets carried around to be the high number: 100. Same chances, still doesn’t leave out any numbers between 1-100, and most of all is easier to read for everyone without hiccups/misreading caused by briefly glancing at results and accidentally thinking a 40 is 30 because that’s what we naturally read 30:0 as.


Oh and Noah, you’re wrong. It’s not 0-100 with his change. It’s still 1-100 because 00 + 0 would equal 10, not zero. So the lowest roll you could have is 00 + 1 = 1 and the highest roll you could have is 90 + 0 = 100. His system is fine, I just find it tedious to do it this way when all it resolves is some OCD about the way a 100 result is calculated.


I arrived at this same conclusion. That it would be more consistent by always considering the 0 on the d10 to be a 10. But honestly, it’s just easier for my players the other way and statistically nothing changes. Either way it’s a 1-100 roll. It’s easier for them to read the dice the common way and remembering the exception that zeros across both is a 100 is also super easy. I find it actually takes more time to do it the “right” way than to do it the “wrong” way. Maybe if it was a custom d10 where the zero really was a 10 on the die itself then it would be easier, but meh. I’m not ocd about it as long as statistically we end up with a proper d100 roll.


The method described on the article is the one I use, it is the only consistent method. With this method, the 00 on the tens die ALWAYS means 0, and the 0 on the units die ALWAYS means 10.


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