It’s one of those heart-stopping moments when you hear your dungeon master say, “Roll for percentage.”
Your favorite character’s fate is hanging in the balance and the only thing that can save him/her is a 1/100 chance. The dice roll comes to a stop and land on  &  land.
Half of the table roars in excitement and the other half groans in pain.
“That totally succeeds!”
“No way, that’s a failure!”
Well, it all depends on how you read the dice. Today, we’re looking at percentile dice and how to actually read the tricky things. Read our guide on how roll and read percentile dice.
What are Percentile Dice?
Percentile dice, as the name suggests, are dice that give a percentage from 1%-100%. Standard percentile dice will never give you a result of 0%.
There are quite a few ways to actually do this using any number of dice, but the typical way this is done is with two 10-sided (2d10) dice or one 100-sided die (1d100).
How Do I Read Percentage Dice?
Standard percentile dice come in a pair; 2D10. One die typically has single-digit values of 0-9 and the other has 10 digit values of 00-90.
When rolling for percentage both dice are rolled at the same time and the results are combined to get your percentage.
There are 2 schools of thought on how to actually read these dice, and I definitely have a preferred version, but for completionists, we’re going to look at both.
Place Value Method
For the Place Value System, the double number die or the 10s die equals the place values 00-90 and the single number die equals the place value 0-9.
 +  = 73%
 +  = 50%
 +  = 9%
It’s just a simple matter of combining the two numbers together.
But what happens when you roll:  +  = ?%
Remember rolling percentile dice will never give you the result of 0% so when you roll 3 zeroes it actually comes out to 100% and depending upon your dungeon master that could be really good or really bad.
 +  = 100%
This is my preferred version of reading percentile dice, and easier to visualize in my head. It’s also the official version of how to read percentile dice in the Dungeons & Dragons handbook 5th edition.
“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.”— D&D Beyond
The other way of reading percentile dice is by looking at them as 2 separate entities and adding them together.
The first die is 00-90 and the second die is 1-10. It looks pretty similar to the previous method until you notice the 1-10.
The single-digit die is treated as its own entity of 1-10 instead of looking at it as a simple place value.
So in the same examples as before:
 +  = 73%
 +  = 60%
 +  = 9%
It’s mostly the same except for  +  = 60%
If you didn’t quite get how that works, the “0” on the single-digit die is treated as a 10. It’s a d10 after all. So they’re added together.
 +  = 10%
 +  = 50%
 +  = 90%
If you’re picking up what I’m putting down then you can see that to get the coveted 100% you need to roll:
 +  = 100%
The addition system is a little older, and if you play a lot of D&D, you’re eventually going to find someone who reads it this way. Either way is completely valid as long as everyone agrees on a set system.
If you still don’t feel comfortable with it you can always download our handy chart and just match up your rolls to the proper percentile.
100 Sided Die
You may ask yourself, “Why do I even bother with 2d10s when there are 100 sided die out there?”
The 100 sided die is actually called a Zocchihedron. The name may ring a few bells because it was designed by Mr. Lou Zocchi, the dice guru himself. He’s one of the pioneers in the industry and studied dice extensively.
He believes that the mass production of dice and using machines to round out the edges creates imperfections during the process. This gives certain die higher probabilities to roll certain numbers. This is why his own brand of dice, Zocchi Dice, is machined and hand-trimmed. They actually come with pretty sharp edges to ensure that every facet of the die has an equal percentage.
The Zocchihedron or the 100 sided die is a little different. It was originally meant to be rolled on a small surface of water so it could float but has since been redesigned to include a core that simulates this. The other problem with the Zocchihedron was the number distribution.
The numbers are wrapped around it like a globe with more numbers wrapped around the equator and fewer numbers around the poles. The first design actually went in order with higher and lower numbers at the poles, but after a study showing how imbalanced it was, Lou Zocchi randomized the numbers for better distribution.
2d20 or 1d100?
Dice edges and fun facts aside, the question remains “Which one is better?”
Mathematically and all other factors considered equal, 2d10s will result in more balanced and accurate rolls in the long run. If we assume that both dice are perfectly symmetrical and balanced in all ways, there is an equal chance for someone to roll 1%-100% with every single roll.
The Zocchihedron or 100-sided die is inherently less symmetrical than 2d10s. It works and is fun, but if you’re looking for even distribution in numbers you’re going to find more balanced rolls with 2d10s.
Of course, if you’re worried about true randomization you can always use a computer program to generate your dice rolls. They’ll be more accurate and random, but it’s just not as fun as rolling and hearing the clatter of dice on the table.
I hope this helps you roll and read your percentile dice. If you have any questions or comments, we’d love to hear them. Drop a comment below!
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