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


All numbers from 1 to 100 have exactly two significant digits. If you use the rules like originally designed you don’t need math at all. No confusion at all. You just roll 2 d10 separately and use one as the left digit and the other as the right digit. The confusion only started when they added the zero, this giving this sense of math required. If instead they had used an underscore there would be no doubt: 0_ & 7 is 07, 5_ & 0 is 50 and 0_ & 0 is 100. This gives the same probability of rolling any number between 1 and 100. Messing the system could mess the probabilities and THEN it would make it INVALID. If only people read and followed the rules…


The easiest method for me is to add the two dice together like I would when rolling any other dice. You don’t need any special rules other than that. When I roll 2d4 and they come up 1 and 2, it is 3 total. No debate needed. When I roll 2d10 and they come up 0 and 0, the total is 20, not 0. Still no debate needed and no genuine confusion between players ever arises there. So we know a 0 on a d10 is a 10. The confusion with d100 comes because 00 on a percentile die is 0. I know this because if I roll a 00 and a 02 it is a 2. What else can it be?

So adding the total of each die together shouldn’t be confusing once you get used to it. Just roll the d10 normally and take the number. Add that to whatever you roll on the percentile die. Just like you add die together every time you play. You will never get the wrong answer and you will have a 1-100 scale without needing to decide beforehand what a 00 and 0 mean. Instead just let them mean what they already mean and add them together.

Preston Waltrip

Percentile dice are very simple. No addition occurs at any stage. What you do with each d10 is generate a single integer and insert it into a specified field in the result.

The d10 generates an integer (0-9) for the units field. The 00-90 die generates an integer (0-9) for the tens field. It is printed 00-90 to make it distinct from the 0-9 die without using a different colour of die. For many years prior to companies printing 00-90 dice, dice sets were sold with two 0-9 dice, one of which would be a different but complementary colour to the rest of the set.

So a 50 & 0 would be 5 in the “tens” field, and a 0 in the units field, with the final result of 50.
A 00 & 0 would be a 0 in the tens field, and a 0 in the units field. The only number between 1-100 where this occurs, is 100. Hence. 00 & 0 is read as 100.

Vaughan Cockell

This is the way it is: 0/00 is just 100 because you can’t roll nothing. Trying to remember that 10+0 is 20 and 30+0 is 40 just doesn’t make sense when looking at the die. You have a 10s digit die and a singles digit die. The single digit die can’t all of a sudden become the 10s digit die. 0/00 is the only exception to the rule and has the same 1% probability every other roll does, rather than breaking the dice continuity rule every time the singles die comes up 0. Get it? Also, rolling 90+0(10) is not a fun crit to roll, seeing 3 zeros is way more fun and shocking “0/00” I CRIT 100!


I sure someone already pointed it out but…PHB page 6: "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.

Double/triple zeros is a 100.

Ben J.

Leave a comment

Please note, comments need to be approved before they are published.