Simulating Reality With Funny-Shaped Dice: The Bystander’s Guide

Perhaps the most iconic symbols of tabletop roleplaying games (RPG’s) are the funny-shaped dice. Even if you’ve never played an RPG, you’ll probably recognize “D&D dice”. But how are they used, and why are there so many different kinds? Let’s talk about that.

Why Do You Even Need Dice?

In last Wednesday’s post, I talked about the fact that RPG’s allow players to have their characters attempt anything at all. It’s up to the gamemaster (DM) to figure out whether the action succeeds or fails, and what happens as a result.

But that creates a huge potential for the DM to rule in a way that’s less than totally impartial. Or at least in a way that seems less than impartial, which is just about as bad. Remember those arguments about who missed in your games of Cops & Robbers as kids? The whole point of RPG rules is to prevent those arguments.

But if the rules call for absolutely cut-and-dried results, so that the outcome of any action was completely predictable, the game would become less about a story, and adventure, and more like a game of chess. That might make an interesting game too, but that wasn’t what the originator of RPG’s wanted. He wanted suspense, and excitement. He wanted the players to have moments when they shouted in triumph, and moments when they groaned in collective dismay. And chess, frankly, is a little shy of those moments.

Randomness Adds Narrative Suspense

Consider the scene in Star Wars: A New Hope when Luke and Leia have to swing on a rope across a chasm in the Death Star. Does the hook catch on the convenient ceiling fixture? Does the rope hold? Can Luke keep his grip? Do they swing the right way, with enough force to make it across? In a movie the audience doesn’t know what will happen, so there’s a moment of suspense as they swing across, and a moment of small triumph when they make it. The screenplay writer knew they’d make it, but adding that challenge created narrative tension for the audience.

In an RPG, the players and DM are the audience. If they can simply calculate the outcome of any action, there’s no suspense. The characters will only do things that will succeed. There’s no tension, there’s no moment of doubt, and no moment of triumph when they succeed. Adding the random result of a die roll to the action restores the doubt, and with it that narrative uncertainty that makes a story interesting. When a character attempts something risky, the DM assesses their chances, factoring in things like skill, conditions, and any special circumstances. Once the chances are determined, the player rolls the dice and the outcome is decided. Luke may have a lot of skill at swinging from ropes, but will it be enough? Will that kiss from the Princess make him hold on a little tighter? Will they make their escape, or plummet to their deaths? Roll the dice and see!

Life is Unpredictable

Consider, too, that from your own point of view, much of life is unpredictable. Think about driving to work. A lot of things could happen on that drive. Does a small child dart out into traffic to chase a ball today? Does anyone run a stop sign and hit your car? Is there a traffic jam?

Hopefully none of those things are an everyday occurrence for you. But any of them could occur on a given day. You might say there’s a chance it could happen.

Now think about how this would work in a game. The DM can’t keep track of every wayward child and distracted driver in the world, or even in the small town where the story is set. Even if he could, it wouldn’t improve the story the DM and players are creating together. So instead, he assigns a probability to some sort of traffic issue. Perhaps once in 20 trips there’s a problem. Now all he has to do is roll some dice to see if this is that trip.

Different Chances, Different Dice

Regular old cubical dice, like the ones you’ve used to play Yahtzee or Monopoly, have six faces (duh) and therefore six possible outcomes. So the smallest non-zero chance of something happening would be 1 in 6, or 16.67%. That isn’t really that small of a chance. If there was a 1 in 6 chance of getting in a car accident every time you drove, would you ever drive?

You could, of course, roll multiple dice. If a car wreck only happened if you rolled two Yahtzee dice and got snake eyes (both rolled a 1), that would be a 1 in 36 chance. Which is substantially better. But if you drive to and from work five days a week, that’s still about a wreck a month.

The other problem is that rolling multiple dice and adding them together results in a bell-shaped probability curve. In some instances that’s a reasonable simulation of reality, but figuring out the probability of a particular outcome can get pretty cumbersome.

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But there’s a simple way to get a linear progression with smaller steps: use dice with more than six faces. Typical RPG dice sets include dice with 4, 6, 8, 10, 12 and 20 sides. Most sets come with two 10-sided dice, because someone figured out that if you used one 10-sided die as a tens digit, and another as the ones digit, you could simulate a 100-sided die, sometimes called “percentile dice”. And so the dice set was born.

A Little Nomenclature

Saying “roll 7 six-sided dice” is a little cumbersome. So gamers developed a shorthand notation: Nd#, where N is the number of dice to roll, and # is the type. So “roll 1d8” means roll one eight-side die. “Roll 3d12” means three 12-sided dice (added together, typically). The 100 sided die (or simulation thereof) is noted as % when written, but at the table you’d just say “roll percentiles”.

The Dice In Practice

To help you understand how this all works in practice, let’s look at the Death Star Chasm scene again. Bear in mind that different games will have different rules about which dice to use, whether you want to roll over or under some number, and how favorable or unfavorable circumstances affect the result. In this example, we’ll assume that for most things you’ll roll 1d20, and the bigger the number the better as far as results go.

Luke wants to swing across the chasm. First he has to throw the grappling hook around something and catch solidly. The rules specify that you need to roll a 15 on 1d20 to succeed, and you can use your character’s athletics or rope handling skill (pick the higher one) as a bonus. Also, your character’s hand-eye coordination matters for this, and if the target is something easy like a pipe you get a +2 bonus for that.

Luke sees a pipe that looks solid enough. He has a +2 bonus at rope handling from his time roping womp rats, but he’s also +5 at athletics, so he uses the +5. He has excellent hand-eye coordination (+4). So altogether he’s at +2 (pipe) +5 (athletics) +4 (coordination), for a total of +11. Luke’s player rolls a d20, and rolls a 5. Oh no! But with the +11, it’s a 16, and he only needed a 15, so the rope catches. Hooray!

Now it’s time to swing across. It’s an athletics roll, and he needs a 11 or better. But he’s carrying the princess, so he’s at -2 for her weight. And she gives him a kiss for luck, so that’s a +1. So the modifiers are +5 athletics, -2 for the princess, but +1 for the kiss, for a total of +4. Luke rolls a 12, for a total of 16, and they make it easily.

So Now You Know!

Now you know what those weird dice are about. Let me know if that made sense to you. And please drop a comment if there’s anything else about role-playing games that you’d like explained.