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?

Back to blog


As mentioned above the 0 00 =100. You don’t want a scale that goes from 0 to 100 you want one that goes from 1 -100. Dice are there to represent luck and chance. You roll them because an event is not clearly predetermined to succeed. So you have your success spectrum let’s say 1-50 and fail spectrum 51 -100. This can also be equal to a 50-50 chance of success. This means you could roll a d20 and 1-10 is fail and 11 -20 is success and expect the same results. You don’t need the 0. After all if count correctly 0 up to 100 that’s 101 numbers and from my math experience a probability can’t never be more than 1 or equivalently more than 100%. Basically use what ever you like the scale from 0 – 99 is the same as 1 -100 but not the same as 0-101


This is not consistent either because you have to use different rules for each die. In the case on the “tens” die, you choose to read the 00 at zero. And in the case of the “ones” die, you choose to read 0 at ten. That is inconsistent. If you read 0 as 10, then 00 should be 100 in order to be consistent. So it also fails. Because you have to have opposite rules for each die. That means it is purely a matter of taste and tradition. And it has been played as 00+0 equals 100 since the beginning so it’s best to stick with that since it is also the quickest way to read most of the numbers.


If you roll a 90 and a 0 (with this system) that would be 100, so the scale is 0-100.


0 and 00 = 100 ….


If you list all combinations of the dice in excel the spread becomes clear with the (00, 0) being the disputed “floating” combination and a convention to be chosen and stuck with: either it’s important for you to know whether there’s a 0% chance of success, or a 100% chance. The former decides that you can’t get 100% chance; the latter decides you can’t get a 0%chance of ‘success’. Choose one and stick with it. Like that every dice roll is clear and either 000 is a hard FAIL or a hard SUCCEED. Being personally of a chaotic penchant, i consider 000 as ‘uncertain’ and a call for a reroll. Like that i stick between 1 and 99%.

Thomas White

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