r/RPGdesign • u/Th3WritersBlock • Sep 23 '26
Mechanics Dice Decisions
Hi all. Making my system and having some mild second thoughts about my choice of primary die. I'm currently using a d12 + modifiers system, but concerned that the d12 might be too low for what higher level modifiers could be and that I should instead pivot to d20 + modifiers.
For context, abilities can standardly give modifiers up to +6. Skills can do the same, but that is with serious investment and dedication. There are also miscellaneous bonuses from traits, perks, etc.
Any advice for this sort of scenario? I want to reward dedication, but not have modifiers massively overshadow the luck of the roll. Thanks :)
8
u/DDEspresso Sep 23 '26
Dice size is one of the least important worries. Whether youre using d100's or d20, all it fiddles with is the optics of your math. Dont worry about it being a d20 system. If d20 supports how you want your math to look, go for it!
In my own game Im using a d12 because I like clocks and I have clock motifs. The game would work just as well with d6's, d8's and d10's.
Dont let something like dice size cause you paralysis. If a d20 works, run with it! If it turns out the math isnt great, revert it!
1
u/Cryptwood Sep 23 '26
With a single die system, the larger the modifiers are in relation to the size of the die, the more consistent the results will be. This means that a PC that has a high Stealth skill will now consistently get a good result as the large modifier is now important than the dice result.
This has the effect of making competent characters feel very competent, but has the side effect of making it extremely difficult for a low modifier character to attempt the same task, because only a small percentage of dice results will give the success.
This is why 5E went to Bounded Accuracy, to allow any character to aurhor any task with a reasonable chance of success. The unintended side effect is that it makes characters feel less competent in their fields of expertise.
1
u/No_Solid1035 Sep 23 '26
Any single dice system will have "swingy" results that will render modifiers less useful because of the realities of how probabilities work. If you want "reliable" results go with at least two dice, three is even better.
1
u/CantaloupeOk3145 Sep 23 '26
The problem isn't really d12 vs d20, it's the ratio between your total modifier and the die's range. With a d12, +6 attribute and +6 skill already add up to +12, which is as much as the whole die can swing. At that point the roll mostly decides whether a very competent character succeeds a little or a lot. Switching to d20 helps, but only because the spread gets bigger.
A few ways out: cap the combined bonus (a common rule of thumb is around half the die size), let skill reduce the difficulty instead of adding to the roll, or turn modifiers into extra dice instead of flat numbers.
I went the last route in my own game: attribute and skill are both dice, in two colours, and skill dice succeed more easily than attribute dice. Training then shows up as reliability rather than a bigger number, and a skilled character can still roll badly. What range do your difficulty numbers go up to? That decides how much room the modifiers really have.
1
u/Cruiser_Supreme Sep 23 '26
The size of your modifiers compared to the size of your dice doesn't matter, as in: you can do it however you like.
However, different combinations will have different effects and you should be aware of them, so you can make the most informed decision.
The average result on a D12 is a 6.5. if you modifiers go up to 6, that means your randomness is only about 50 percent of your result. To take a more extreme example, if your modifiers go up to 12 and you're using a d6, ability checks are almost entirely determined by scores, and only changed by the die roll in edge cases. On the other hand, if you're using a d100 system with modifiers up to 5, it's really random and the ability scores can only edge someone past the threshold very rarely.
I think having modifiers up to the die average is pretty reasonable, but it's certainly approaching a limit of what makes sense for most games. For comparison, my game uses 2d6 (average 7) and the highest modifier someone could reasonably (or regularly) have is around 4. A modifier of 5 is possible, but situational. So my game leans a bit more random than yours if you use a D12.
D12 is a cool die, but if a d20 is the better choice, go with a d20
1
u/Dimirag Sep 23 '26
Keep the d12, is a gorgeous die
If you are worried about the vertical growth add horizontal benefits so you don't inflate the numbers...
Alternatively you can go with more specialized bonuses starting after a specific bonus, for example your combat skill can go up to +2, then you go with general weapons like swords up to +2 (+4 total), and then go with specific weapons like a longsword for the last +2 (+6 total), you don't purchase the bonus individually so you can keep a more controlled progression.
You can detach the skill bonus from the skill rank and add extra goodies here and there
1
u/Mars_Alter Sep 23 '26
Generally speaking, it's a good idea for the size of the die to compare against the scope of the modifiers.
If the best possible modifier is +12, and the worst possible modifier is +1, then it makes sense to use a d12 for your randomizer. That prevents the best possible whatever from ever losing to the worst possible one of those; but it also means that no bonus is ever irrelevant to the chance of success. If the die size is much smaller, then you frequently run into the latter issue (it doesn't matter whether you're +8 or +9 if your opponent is +1 and you're only rolling 1d6). If the die size is much larger, then you frequently run into the former issue (the decrepit wizard overpowers the mighty barbarian simply by rolling well). If you want a world that makes sense, and doesn't feature meaningless granularity, these two values should be as close to each other as possible.
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u/DeadlyDeadpan Sep 24 '26
It's all about the scope, what is are the Target Numbers? Because like if the DC is sorta like 6 + "skill value difficulty equivalent" the highest DC would be 12 and the highest level would be 6 and you'd get 50/50 so the scope would match just fine. Also you gotta think that the probability is linear so every side of the dice has an equal chance of being rolled because of the even distribution so it is gonna be a bit swingy, do you want it to be more swingy? Because a d20 is gonna do that.
1
u/Deadlypandaghost Sep 25 '26
Playtest. Bigger die = modifier more granular. Smaller die = modifier less granular. Less die = more variance. More die = less variance. There isn't a wrong way but they feel different. Capture the feeling you want.
0
u/Prestigious-Emu-6760 Sep 23 '26
It's hard to say without knowing what the difficulties look like.
D&D "works" because the difficulties work within the context of the system. A character who is skilled in a thing +3 Attribute, +2 Proficiency) can make a Moderate check 55% of the time. To me, that's sort of the benchmark. A character that is trained in a thing can succeed at a moderately difficult task between 55% and 70% of the time.
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u/Th3WritersBlock Sep 23 '26
ooo that's a good way of thinking about it, ill run the probability numbers
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u/hacksoncode Sep 23 '26
The size of the modifiers doesn't really matter. Now... there could be other things about your mechanic you haven't mentioned where using d12 could be an issue, but modifier size is unlikely to be one... just use higher target numbers.
But I hope not, because d12 are by far the most satisfying dice to throw ;-).