So, you need a critical hit or a massive loot drop table result, and you've got to roll 100 sided dice to make it happen. Most people just grab two ten-siders and hope for the best without thinking about the math or the physics. It feels simple. Yet, if you’ve ever been at a table where a player argues over whether a "00" and a "0" means zero or one hundred, you know the chaos this "simple" roll creates.
Rolling a d100—often called a percentile roll—is the backbone of legendary systems like Call of Cthulhu, Warhammer Fantasy Roleplay, and the classic RuneQuest. It’s the ultimate arbiter of fate. It’s brutal.
✨ Don't miss: Why Pics of Rubik's Cube Always Look Better Than Yours
The Physical d100 vs. The Percentile Pair
Let's be honest for a second. The physical 100-sided die, often called a Zocchihedron, is basically a golf ball. Invented by Lou Zocchi and released around 1985, it doesn't really "roll" so much as it "drifts" across the table for three minutes before eventually settling on a number. If your table is even slightly tilted, you're doomed.
Most veterans hate the Zocchihedron.
Instead, we use two d10s. One represents the tens digit, the other the ones. It’s efficient. It’s fast. But even this has a learning curve that trips up beginners. You have to designate which is which before the shake. If you don't, and you see a 7 and a 2, you’ll naturally want the 72 if you need high, or the 27 if you need low. That’s cheating. Don't be that person.
Reading the "00" Mystery
This is where friendships end. Most percentile sets come with one die numbered 0-9 and another numbered 00-90.
If you roll a 70 and a 5, that’s a 75. Easy.
If you roll a 00 and a 7, that’s a 7.
But what happens when you roll a 00 and a 0?
📖 Related: Monopoly GO New Year's Treasures: What Most Players Get Wrong
In almost every gaming system ever written, from Dungeons & Dragons to BRP, a "00" and a "0" is 100. It is never zero. You cannot roll a zero on a 100-sided die. It’s the "natural 20" of the percentile world, except usually, in games like Call of Cthulhu, rolling a 100 is the worst thing that can possibly happen to your character's sanity or physical health.
Why Percentile Systems Feel Different
Flat math. That’s why we do this.
When you roll a d20, every number has a 5% chance of appearing. When you roll 2d6, you get a bell curve; you’re much more likely to roll a 7 than a 2 or a 12. But when you roll 100 sided dice, every single outcome from 1 to 100 has exactly a 1% probability.
There is no "average" result you can rely on.
This creates a high-tension environment. If your "Medicine" skill is 40%, you know exactly what your odds are. There’s no mental math required to figure out if a +2 bonus is worth it. You either have the 40% chance or you don't. This transparency is why investigators in horror RPGs prefer it; the looming 99% or 100% "Fumble" range is a constant, terrifying reality that doesn't care about your character level.
Digital Alternatives and True Randomness
A lot of us have moved to VTTs (Virtual Tabletops) like Roll20 or Foundry. Or maybe you're just using a Google search bar.
When you type "roll d100" into a browser, you're using a Pseudo-Random Number Generator (PRNG). For 99.9% of gamers, this is fine. It’s "random enough." However, if you are a statistics nerd or a high-stakes DM, you might care about the "pseudo" part. These algorithms use a "seed" (often the current system time in milliseconds) to run a mathematical formula that spits out a number.
If you want "True Randomness," you’d need something like ANU QRNG, which uses vacuum fluctuations of the quantum magnetic field to generate numbers. Is that overkill for a goblin encounter? Probably. Is it cool? Absolutely.
Common Mistakes When Rolling Large Dice
I’ve seen it a thousand times. A player picks up two identical d10s—same color, same ink—and rolls them. They get a 4 and a 8.
"Which one was the tens digit?" the DM asks.
"Uh... the left one?"
The "Left-to-Right" rule is a recipe for disaster. Dice bounce. They cross over each other. If you’re going to roll 100 sided dice using two d10s, use high-contrast colors. Red is tens, Blue is ones. No ambiguity. No arguments.
Another mistake? Rolling on a soft surface. If you’re rolling a Zocchihedron on a felt dice tray with too much padding, it won't settle. These dice need a hard, flat surface to actually stop. Otherwise, it just wobbles until someone gets frustrated and taps it, which—again—is cheating.
The History of the 100-Sided Result
We haven't always had these plastic polyhedrals. Back in the early 70s, before d10s were even common, gamers used to use 20-sided dice numbered 0-9 twice. They’d color one set of 0-9 with a crayon to indicate the "tens."
We’ve come a long way.
The move toward d100 systems was a move toward realism. Designers in the late 70s felt that the 5% increments of a d20 were too "swingy" and granular. They wanted a system where a character could improve by just 1% or 2%. It allowed for a sense of progression that felt earned rather than gifted by a level-up screen.
Practical Tactics for Your Next Session
If you’re the Game Master, don’t over-call for these rolls. A d100 roll is a moment of high drama. Use it for:
- Random encounter tables with 100 unique possibilities.
- Percentile chances for weather changes.
- Critical hit or fumble effects that require specific, rare outcomes.
For players, the best thing you can do is buy a dedicated percentile set. Most dice shops sell them together. The "tens" die will have the extra zero (10, 20, 30...). It saves so much time.
Actionable Steps for Better Rolling
- Invest in a "Tens" Die: Stop using two standard d10s. Buy a specific percentile die (the one with 00-90) to eliminate any "which is which" arguments.
- The "100" Rule: Establish at the start of the session that 00-0 equals 100. Write it on a sticky note if you have new players.
- Tray Dynamics: If using a spherical d100, use a large, flat-bottomed tray. Avoid small circular trays where the die will just spin indefinitely.
- Digital Validation: If you suspect your physical dice are unbalanced (it happens with cheap manufacturing), perform a salt-water float test or simply switch to a verified digital roller for high-stakes moments.
- Check the System: Remember that in games like Black Crusade or Eclipse Phase, you usually want to roll under your skill, not over. Know your target before the dice hit the table.
Rolling 100-sided dice is about more than just finding a number. It's about the 1% chance of a miracle or a disaster. Respect the math, clear the table space, and make sure everyone agrees on what the "00" means before you let it fly.