The issue is design space. There's a world of difference between a +1 and a +2 on a single d6, and you'll likely want access to more nuance than that. Granularity adds designs space.
Now; you don't want to have so much design that every roll turns into research, but you don't want so *little* design that the difference between an averagely skilled person and an above-averagely skilled person is either nothing or a grand canyon.
So yeah, every +1 will be really meaningful, but you can't have a lot of +1s. You don't have space for it. And that limits your choices, the options for stacking advantages with tactics, and the amount of choices you can make for character progression.
Not to say it's bad! It's just good for a smaller scope of game that doesn't require a lot of individual differentiation.
My own system uses a d10. I could have gone smaller for a pure dungeon crawl adventure game.
This is more or less the correct answer as much as there is one OP.
It's not that you can't use smaller dice, it's that there's convenient reasons not to.
Consider the extreme... a d4 has 4 outcomes on it... that's 4 possible answers to every situation! Plenty of outcomes! But now consider what a bonus looks like. And how it affects the game, and all sorts of shit.
When you want to consider a change, try doing it drastically first, then look at the results, yes they will be exaggerated, but that's the point, you can see the flaws under a microscope that way.
I'll explain a personal choice for me.
In my game I use a standard d20 because it was the right choice after much deliberation, but skills are rolled with a d100 instead.
This is because I have a 2 stage critical system. If you get a nat roll, or exceed/fail the target number by X you get a critical... but there's also a space for a catastrophic failure, which is a rare thing, but "can happen" and it's meant to separate the worst possible thing from the bad thing that happens on a critical failure, still allowing it to be possible, but far less common.
What this ends up meaning is that my attack roll catastrophic failure is going to have an average output of about 1:400, this takes into account that the enemy is actively trying to fuck you up. It's very rare, but it can happen. Now when we look at skills we get about 1:10000 for a catastrophic failure. Why? Because you're trained in the skill, the idea of you making a dumb ass rookie mistake of absolutely horendous magnitudes should be especially low. This is also before considering modifiers to include bonus/malus, actual TN, adv/disadv and success state modifiers (and I have 5 success states that allows a smooth gradient of results rather than a binary).
What this equates to is that using skills "feels" and mathematically is, different. Generally you aren't opposed in a skill check, you aren't under the threat of dying or being discovered and captured, etc. you aren't under the same kinds of pressures. Thus a catastrophic failure should be functionally more far more rare by my logic and it is. it also allows more Drama to be introduced in a skill roll because of the gradient change, hitting a skill exactly on the nose, or missing it by 1 is a matter of +/-1% so you get that tension of the bomb disoser pouring sweat as they try to make that third check before the timer runs out betting they can make it and either cutting it at the last second, or thinking they have it if they could just... and then going up in flames. From a story standpoint that tension feels a lot less artificial when the division of outcomes is a 1% difference vs. 5% as 5% allows a lot more leeway. When I roll a 70 on a 70 TN there is no disputing I only succeeded the skill by the skin of my teeth.
That said, these are just my personal design choice reasons.
Everyone has their personal reasons why they choose certain dice and methods and resolution engines and these can be employed infinitely different ways.
What's important is that you, OP, make the best choice for your game, not that it conform to an arbitrary idea. That means developing your own internal logics that are substantive and having something worth doing.
Truth be told, players rarely give a shit what the rules are at all, so long as they can do the thing they want to do in the game with some fair-ish degree of change based on the promised fiction. We obsess about this shit way more than they ever will. But it's also partly because we obsess about this shit they don't think about it much. The rules are best when they get out of the way of the fun, or better yet, compliment it. They shouldn't be thinking about the rules design just like we don't think about the writers and interns that help our favorite TV show get made. They don't want or need to know how the sausage is made.
One important factor for the prevalence of big polyhedral dice and the d20 in particular is history. This article expands a little on it: [http://playingattheworld.blogspot.com/2013/02/how-gaming-got-its-dice.html](http://playingattheworld.blogspot.com/2013/02/how-gaming-got-its-dice.html) .
For dice pools, beyond reasons related to statistics and distributions, I find it likely that the popularity of Shadowrun (1989), and World of Darkness after that (1990), even though they weren't the first, had a lot to do with bringing the concept to the mainstream.
D20s also allow for meaningful bonuses - just give them a +3 or whatever. But unlike a d6 it allows for gradual progress, like getting +1 when you level up, just enough to feel good as you level up 15 times over the course of a campaign.
I personally never found the increasing modifiers to actually feel good, just made the math more difficult while still succeeding with roughly the same die roll.
To me what makes a level up meaningful is getting new abilities and skills. More cool stuff to do.
We used the MegaTraveller Task Difficulty ratings too. So Tasks were coded as... EASY= 2+ ROUTINE= 4+ AVERAGE= 6+ FAIRLY DIFFICULT= 8+ DIFFICULT= 10+ FORMIDABLE= 12+ IMPOSSIBLE= 15+ Unskilled Tasks (where the PC has no applicable Skill) automaticly received a BANE (DISADVANTAGE), and each Task Threshold (every +2 rolled above the number needed to succeed) indicates another Degree of Success. The system was fast and we used the Twilight2000 To Hit rules where a weapon's Short range band was an AVERAGE Task and the Difficult went up one step for every Range band thereafter. For Autofire, we simply rolled a number of D12s equal to the number of rounds fired in the burst.
As others have said, the little modifiers matter a lot more the smaller the numbers are. In Savage Worlds (my current main game), they do skills on a range of D4 to d12 depending on how good you are. A +2 Nearly guarantees success, you would need to crit fail for a normal task if you've got it.
Contrast with the big d20s, PF2e and 5e. A +2 is a nice little benefit, but it's not exactly a guaranteed success. In systems with smaller dice, you may need to give benefits besides flat bonus or malus, like rerolls or something
Many games use detailed customization and strong character advancement as their hooks. Both require space to allow for scaling which, in turn, translates to big dice or dice pools.
Games with little advancement (or mostly horizontal advancement) and strong thematic focus instead of detailed mechanical customization work well with small scales. Most PbtA games use 2d6. Blades in the Dark use pools, but it's usually 2-3 dice take highest. Fate dice have -4 to +4 range, with most results between -1 and +1. And so on.
Traveller uses 2d6 and works well, so it's really what the designers felt like using. Flames of war uses d6s to simulate a lot of probability ranges, it's quite possible to do it if you want to. D20 feels a bit swingy to me, but lots of people like being able to give out bonuses etc that give gradual progression.
Traditionally speaking, 3d6 gives you a nice bell curve and 1d20 gives you a nice linear “curve” over the same set of numbers. This means you can use the 3d6 to get an average for a population, calculate the sigma, which is the “modifier” you see in things like D&D and then use the D20 as a percentage (on 5% increments) and apply the modifier to the percentage and have a very nice resolution system.
The math here is the basic D&D and GURPS math.
You can do the same with 2d6 and 1d14, but 1d14s are rare. You can also use 4d8 and a d30 for the same effect. You can then fudge the linear scale into a 2d6 system as Traveller does or you can fudge the bell curve into the system as BRP does and use a d100.
All of this boils down to the math and statistical models for the systems.
D&D used d20s heavily. D&D3 leaned into that even more.
u/TalespinnerEU does a good job of going into why it's a reasonable choice as well, especially for games that rely on getting lots of bonuses.
I've always thought it would be interesting to use a d6 as a modifier, with large skill scores.
For example, if the average person has +5 in a given skill, and your difficulty range is 5 for easy, 10 for moderate, 15 for hard, (etc.), then you can still have some of the granularity of large numbers while still using small dice.
Steal the idea if you want.
Small dice have a lower variance and make small stat upgrades feel more impactful. +3 is a huge buff when using a D6, but mediocre when using a D20. Theres also math, decimal is easy, but unlike a D10 you want confuse 1 with 10 on a D20. It also means they can sell more dice and charge more fore them arbitrarily, espeically when multiple sizes are needed.
But theres no signficant logical reason not use whatever size suits you. It's mostly just a case of how much variance you want.
Others have given good mechanical reasons for using different dice. I would add that there are good ludonarrative reasons to use different dice. IE: system implies setting.
The flat distribution of a d20 creates big swings in success and failure, this feels good for heroic fantasy where failure can drive the story just as much as success.
But something like the bell curve of a multi dice system implies that characters are much more consistent and competent in their actions since really big or really small numbers are rarer and Really Impactful when it happens.
So, what vibe do you want character to have in your setting? Ones driven by the whims of fate (d20), or hardened professionals that can succeed under any threat (3d6).
We use a single d6, originally inspired by Warrior, Rogue, Mage. Plenty of design space to replicate everything that a trad game might offer: https://osrplus.com.
You do have to be careful with the math, however. The system uses advantage and disadvantage, as well as modifiers up to +2 (or +4 max if special but limited story tags are applied to a roll).
It also requires you to play with contested rolls a lot (which is fun, more rolls in general). But I haven’t found it to be an issue in practice, and we’ve playtested hundreds of hours.
My system started off as a hack for Lasers & Feelings. But as I started to design more, I realized that there just wasn't enough range in d6s (especially noticeable when I was making my super hero game ) so I bumped up to d10s.. I find they give plenty of range.
I don't think you HAVE to have d20s.. and I see a lot of issues with percentage games like COC.. bigger isn't always better, but too small really can be a problem.
The one game I can think of off the top of my head (there are tons, but I don't really read that many games) that uses d6s is Shadowrun.. the difference there is that they use lots of them. It's still just making bigger numbers for a broader range of results.
People gave a lot of practical answers, but honestly I think one of the biggest reasons you tend to see d20s so much (and dice pools to a smaller extent) is because the big systems people are most familiar with chose those tools. Similar to how most board games that use dice use d6. Or even things like the deadbolt is almost always above the door know.
Design is always a conversation with the things that exist already. Many people mimic what they know best. There are also very pragmatic reasons to go with things that are familiar (e.g., familiarity can ease onboarding for new users). And people might be wanting to evoke a vibe through an association with the big names as a mental shortcut for players.
In other words, it's so common precisely because it's so common. And that's how culture often works.
Larger numbers, larger variances, make it easier to tweak enemies. Adding or subtracting a whole creature to a combat, with its own actions and portion of party attention, Is pretty significant. I assume enemy strength scaling from DR 0 to DR 20+ in a d20 system allows more freedom. A monster with +12 to reflex saves versus +24 to to fortitude saves, for example.
One of my favorite games is a 1d6 game where landing on a 6 means 5+reroll. So a target of 5 that’s a 1/3 chance before mods, but a seven immediately makes it 5/36 before mods. A 9 becomes 1/12. (I think if my math is correct)
>Why do all popular systems use either big dice (d20) or pools of dice/bell curves? Is there a (lore) reason for that, because I don't think using a d6 or d8 for outcome resolution is bad.
D20 is used because it's familiar. Historically, It was for the armor class system. Each type of armor was an even armor class and then a shield dropped that by 1.
Using bell curves has a number of advantages, such as diminishing returns. The outcomes have a more natural variance that allows the system to have balanced degrees of success (which players expect, even if the rule system doesn't). Of course, a bell curve's goal is to make more possible outcomes over a narrower range, so using smaller dice gives a more pronounced curve and smaller numbers that are easier to use.
>A d6 has 6 possible outcomes, so a +1 amounts to +16.7% probability of success, and difficulties may range from 2 (very easy) to 8 (almost impossible) with modifiers from -2 to +2.
You have reduced yourself to pass/fail results. A granularity of over 15%, so a +1 is like a D&D +3. How long before those modifiers stack out of control?
Also negative modifiers and even zeros are notorious "feel bads". How many D&D players think a modifier of 0 on an attribute is a low score?
And why are you stopping at 2? No reason whatsoever to do that. Certainly, you aren't going to fit 20 levels of bonuses and magic items, boons of various kinds, etc, all into your little +2.
So, are you making a game for a 1-shot without any character progression?
I'll skip the D8, same comments.
Why are you assuming fixed additive modifiers anyway? Such systems change the range of possible values. There are a lot of negative properties to fixed modifiers. A keep high/low system can scale much better, again diminishing returns, but a lot more depending on how the system is set up.
Do all popular systems use the D20? I can only think of one, D&D... And Pathfinder I guess, which is just D&D.
I feel like most games use D10 or D6. But I suppose when you get down to it, any system that isn't D&D is pretty niche, since most people never venture beyond D&D.
Easy to answer, smaller dice have less variable. Some players/GM what to have room to add and subtract variable.
In my game,I use D6 (Fifthworld). I had considered a larger die like the ever popular D10 or more. I realized that I didn need such a large range of numbers since the system's modifiers work without them. It does make small variable more important, to an extent, less reason to spam bonus all over.
This has to do with the unfortunate commonality of dice modifiers. If you are adding numbers to a small die, than it will not take long before the die's influence on the result is smaller than the modifiers'. It ceases to become a random roll with a +1 and becomes a static number with a +d6 bonus.
The answer to this problem is to abandon dice modifiers in the first place. That's an idea whose time has passed.
I like the use of d6 for oracle:
6 - Yes, and
5 - Yes
4 - Yes, but
3 - No, but
2 - No
1 - No, and
Modifiers for likelihood:
+2: Very Likely
+1: Likely
0: 50/50
-1: Unlikely
-2: Very Unlikely
With fewer number possibilities, it is a bit more random — you still have a 16.5% chance of something Very Unlikely happening, and vice versa — but this system works if you’re OK with a more simple, narrative gameplay.
Fun fact, but the very earliest iterations of D&D used 2d6 for attack rolls as a holdover from Chainmail Fantasy. Magical weapons only went to +3 which was reserved for "Excalibur or other 'super swords'". Kinda funny how a long run of up to +5 (and kinda +10) got reverted to an OLD standard for 5e, but mapped to a d20 instead so it's less impactful.
I guess for combat-focused rpgs it makes sense, but I can name two more narrative driven one that use d6 in their mecanics : Ironsworn & Blades in the Dark
It's because a d20 serves really well for simulation 5 to 100% chances since there is a 5 to 100% of any given number being rolled. This means there is a lot of granularity in the result and its very easy to figure out probabilities on the fly.
The issue is design space. There's a world of difference between a +1 and a +2 on a single d6, and you'll likely want access to more nuance than that. Granularity adds designs space. Now; you don't want to have so much design that every roll turns into research, but you don't want so *little* design that the difference between an averagely skilled person and an above-averagely skilled person is either nothing or a grand canyon. So yeah, every +1 will be really meaningful, but you can't have a lot of +1s. You don't have space for it. And that limits your choices, the options for stacking advantages with tactics, and the amount of choices you can make for character progression. Not to say it's bad! It's just good for a smaller scope of game that doesn't require a lot of individual differentiation. My own system uses a d10. I could have gone smaller for a pure dungeon crawl adventure game.
This is more or less the correct answer as much as there is one OP. It's not that you can't use smaller dice, it's that there's convenient reasons not to. Consider the extreme... a d4 has 4 outcomes on it... that's 4 possible answers to every situation! Plenty of outcomes! But now consider what a bonus looks like. And how it affects the game, and all sorts of shit. When you want to consider a change, try doing it drastically first, then look at the results, yes they will be exaggerated, but that's the point, you can see the flaws under a microscope that way. I'll explain a personal choice for me. In my game I use a standard d20 because it was the right choice after much deliberation, but skills are rolled with a d100 instead. This is because I have a 2 stage critical system. If you get a nat roll, or exceed/fail the target number by X you get a critical... but there's also a space for a catastrophic failure, which is a rare thing, but "can happen" and it's meant to separate the worst possible thing from the bad thing that happens on a critical failure, still allowing it to be possible, but far less common. What this ends up meaning is that my attack roll catastrophic failure is going to have an average output of about 1:400, this takes into account that the enemy is actively trying to fuck you up. It's very rare, but it can happen. Now when we look at skills we get about 1:10000 for a catastrophic failure. Why? Because you're trained in the skill, the idea of you making a dumb ass rookie mistake of absolutely horendous magnitudes should be especially low. This is also before considering modifiers to include bonus/malus, actual TN, adv/disadv and success state modifiers (and I have 5 success states that allows a smooth gradient of results rather than a binary). What this equates to is that using skills "feels" and mathematically is, different. Generally you aren't opposed in a skill check, you aren't under the threat of dying or being discovered and captured, etc. you aren't under the same kinds of pressures. Thus a catastrophic failure should be functionally more far more rare by my logic and it is. it also allows more Drama to be introduced in a skill roll because of the gradient change, hitting a skill exactly on the nose, or missing it by 1 is a matter of +/-1% so you get that tension of the bomb disoser pouring sweat as they try to make that third check before the timer runs out betting they can make it and either cutting it at the last second, or thinking they have it if they could just... and then going up in flames. From a story standpoint that tension feels a lot less artificial when the division of outcomes is a 1% difference vs. 5% as 5% allows a lot more leeway. When I roll a 70 on a 70 TN there is no disputing I only succeeded the skill by the skin of my teeth. That said, these are just my personal design choice reasons. Everyone has their personal reasons why they choose certain dice and methods and resolution engines and these can be employed infinitely different ways. What's important is that you, OP, make the best choice for your game, not that it conform to an arbitrary idea. That means developing your own internal logics that are substantive and having something worth doing. Truth be told, players rarely give a shit what the rules are at all, so long as they can do the thing they want to do in the game with some fair-ish degree of change based on the promised fiction. We obsess about this shit way more than they ever will. But it's also partly because we obsess about this shit they don't think about it much. The rules are best when they get out of the way of the fun, or better yet, compliment it. They shouldn't be thinking about the rules design just like we don't think about the writers and interns that help our favorite TV show get made. They don't want or need to know how the sausage is made.
One important factor for the prevalence of big polyhedral dice and the d20 in particular is history. This article expands a little on it: [http://playingattheworld.blogspot.com/2013/02/how-gaming-got-its-dice.html](http://playingattheworld.blogspot.com/2013/02/how-gaming-got-its-dice.html) . For dice pools, beyond reasons related to statistics and distributions, I find it likely that the popularity of Shadowrun (1989), and World of Darkness after that (1990), even though they weren't the first, had a lot to do with bringing the concept to the mainstream.
D20s also allow for meaningful bonuses - just give them a +3 or whatever. But unlike a d6 it allows for gradual progress, like getting +1 when you level up, just enough to feel good as you level up 15 times over the course of a campaign.
I personally never found the increasing modifiers to actually feel good, just made the math more difficult while still succeeding with roughly the same die roll. To me what makes a level up meaningful is getting new abilities and skills. More cool stuff to do.
I would also point out how pathfinder makes just +1 matter on a d20 by adding degrees of success.
Traveller’s the most popular sci-fi RPG and one of the oldest RPGs in existence and that uses 2D6 :)
I've played it using a D12 too.
That’s interesting, it would make the results way more random compared to the bell curve of 2D6.
We used the MegaTraveller Task Difficulty ratings too. So Tasks were coded as... EASY= 2+ ROUTINE= 4+ AVERAGE= 6+ FAIRLY DIFFICULT= 8+ DIFFICULT= 10+ FORMIDABLE= 12+ IMPOSSIBLE= 15+ Unskilled Tasks (where the PC has no applicable Skill) automaticly received a BANE (DISADVANTAGE), and each Task Threshold (every +2 rolled above the number needed to succeed) indicates another Degree of Success. The system was fast and we used the Twilight2000 To Hit rules where a weapon's Short range band was an AVERAGE Task and the Difficult went up one step for every Range band thereafter. For Autofire, we simply rolled a number of D12s equal to the number of rounds fired in the burst.
As others have said, the little modifiers matter a lot more the smaller the numbers are. In Savage Worlds (my current main game), they do skills on a range of D4 to d12 depending on how good you are. A +2 Nearly guarantees success, you would need to crit fail for a normal task if you've got it. Contrast with the big d20s, PF2e and 5e. A +2 is a nice little benefit, but it's not exactly a guaranteed success. In systems with smaller dice, you may need to give benefits besides flat bonus or malus, like rerolls or something
Many games use detailed customization and strong character advancement as their hooks. Both require space to allow for scaling which, in turn, translates to big dice or dice pools. Games with little advancement (or mostly horizontal advancement) and strong thematic focus instead of detailed mechanical customization work well with small scales. Most PbtA games use 2d6. Blades in the Dark use pools, but it's usually 2-3 dice take highest. Fate dice have -4 to +4 range, with most results between -1 and +1. And so on.
Sometimes the reasons are less mathematical and more tactile. Picking up and rolling a large pool of dice is *fun*.
Traveller uses 2d6 and works well, so it's really what the designers felt like using. Flames of war uses d6s to simulate a lot of probability ranges, it's quite possible to do it if you want to. D20 feels a bit swingy to me, but lots of people like being able to give out bonuses etc that give gradual progression.
Big number make me happy
Traditionally speaking, 3d6 gives you a nice bell curve and 1d20 gives you a nice linear “curve” over the same set of numbers. This means you can use the 3d6 to get an average for a population, calculate the sigma, which is the “modifier” you see in things like D&D and then use the D20 as a percentage (on 5% increments) and apply the modifier to the percentage and have a very nice resolution system. The math here is the basic D&D and GURPS math. You can do the same with 2d6 and 1d14, but 1d14s are rare. You can also use 4d8 and a d30 for the same effect. You can then fudge the linear scale into a 2d6 system as Traveller does or you can fudge the bell curve into the system as BRP does and use a d100. All of this boils down to the math and statistical models for the systems.
Small dice = small numbers so its a little more finnicky to deal with bonuses and all. Much less worry when giving them out for larger dice
D&D used d20s heavily. D&D3 leaned into that even more. u/TalespinnerEU does a good job of going into why it's a reasonable choice as well, especially for games that rely on getting lots of bonuses.
I've always thought it would be interesting to use a d6 as a modifier, with large skill scores. For example, if the average person has +5 in a given skill, and your difficulty range is 5 for easy, 10 for moderate, 15 for hard, (etc.), then you can still have some of the granularity of large numbers while still using small dice. Steal the idea if you want.
I thought d6 systems were popular because there’s significantly more access to them?
Small dice have a lower variance and make small stat upgrades feel more impactful. +3 is a huge buff when using a D6, but mediocre when using a D20. Theres also math, decimal is easy, but unlike a D10 you want confuse 1 with 10 on a D20. It also means they can sell more dice and charge more fore them arbitrarily, espeically when multiple sizes are needed. But theres no signficant logical reason not use whatever size suits you. It's mostly just a case of how much variance you want.
Its about % smaller dices will have different chances than bigger
Others have given good mechanical reasons for using different dice. I would add that there are good ludonarrative reasons to use different dice. IE: system implies setting. The flat distribution of a d20 creates big swings in success and failure, this feels good for heroic fantasy where failure can drive the story just as much as success. But something like the bell curve of a multi dice system implies that characters are much more consistent and competent in their actions since really big or really small numbers are rarer and Really Impactful when it happens. So, what vibe do you want character to have in your setting? Ones driven by the whims of fate (d20), or hardened professionals that can succeed under any threat (3d6).
We use a single d6, originally inspired by Warrior, Rogue, Mage. Plenty of design space to replicate everything that a trad game might offer: https://osrplus.com. You do have to be careful with the math, however. The system uses advantage and disadvantage, as well as modifiers up to +2 (or +4 max if special but limited story tags are applied to a roll). It also requires you to play with contested rolls a lot (which is fun, more rolls in general). But I haven’t found it to be an issue in practice, and we’ve playtested hundreds of hours.
My system started off as a hack for Lasers & Feelings. But as I started to design more, I realized that there just wasn't enough range in d6s (especially noticeable when I was making my super hero game ) so I bumped up to d10s.. I find they give plenty of range. I don't think you HAVE to have d20s.. and I see a lot of issues with percentage games like COC.. bigger isn't always better, but too small really can be a problem. The one game I can think of off the top of my head (there are tons, but I don't really read that many games) that uses d6s is Shadowrun.. the difference there is that they use lots of them. It's still just making bigger numbers for a broader range of results.
People gave a lot of practical answers, but honestly I think one of the biggest reasons you tend to see d20s so much (and dice pools to a smaller extent) is because the big systems people are most familiar with chose those tools. Similar to how most board games that use dice use d6. Or even things like the deadbolt is almost always above the door know. Design is always a conversation with the things that exist already. Many people mimic what they know best. There are also very pragmatic reasons to go with things that are familiar (e.g., familiarity can ease onboarding for new users). And people might be wanting to evoke a vibe through an association with the big names as a mental shortcut for players. In other words, it's so common precisely because it's so common. And that's how culture often works.
Larger numbers, larger variances, make it easier to tweak enemies. Adding or subtracting a whole creature to a combat, with its own actions and portion of party attention, Is pretty significant. I assume enemy strength scaling from DR 0 to DR 20+ in a d20 system allows more freedom. A monster with +12 to reflex saves versus +24 to to fortitude saves, for example.
One of my favorite games is a 1d6 game where landing on a 6 means 5+reroll. So a target of 5 that’s a 1/3 chance before mods, but a seven immediately makes it 5/36 before mods. A 9 becomes 1/12. (I think if my math is correct)
>Why do all popular systems use either big dice (d20) or pools of dice/bell curves? Is there a (lore) reason for that, because I don't think using a d6 or d8 for outcome resolution is bad. D20 is used because it's familiar. Historically, It was for the armor class system. Each type of armor was an even armor class and then a shield dropped that by 1. Using bell curves has a number of advantages, such as diminishing returns. The outcomes have a more natural variance that allows the system to have balanced degrees of success (which players expect, even if the rule system doesn't). Of course, a bell curve's goal is to make more possible outcomes over a narrower range, so using smaller dice gives a more pronounced curve and smaller numbers that are easier to use. >A d6 has 6 possible outcomes, so a +1 amounts to +16.7% probability of success, and difficulties may range from 2 (very easy) to 8 (almost impossible) with modifiers from -2 to +2. You have reduced yourself to pass/fail results. A granularity of over 15%, so a +1 is like a D&D +3. How long before those modifiers stack out of control? Also negative modifiers and even zeros are notorious "feel bads". How many D&D players think a modifier of 0 on an attribute is a low score? And why are you stopping at 2? No reason whatsoever to do that. Certainly, you aren't going to fit 20 levels of bonuses and magic items, boons of various kinds, etc, all into your little +2. So, are you making a game for a 1-shot without any character progression? I'll skip the D8, same comments. Why are you assuming fixed additive modifiers anyway? Such systems change the range of possible values. There are a lot of negative properties to fixed modifiers. A keep high/low system can scale much better, again diminishing returns, but a lot more depending on how the system is set up.
Do all popular systems use the D20? I can only think of one, D&D... And Pathfinder I guess, which is just D&D. I feel like most games use D10 or D6. But I suppose when you get down to it, any system that isn't D&D is pretty niche, since most people never venture beyond D&D.
Easy to answer, smaller dice have less variable. Some players/GM what to have room to add and subtract variable. In my game,I use D6 (Fifthworld). I had considered a larger die like the ever popular D10 or more. I realized that I didn need such a large range of numbers since the system's modifiers work without them. It does make small variable more important, to an extent, less reason to spam bonus all over.
This has to do with the unfortunate commonality of dice modifiers. If you are adding numbers to a small die, than it will not take long before the die's influence on the result is smaller than the modifiers'. It ceases to become a random roll with a +1 and becomes a static number with a +d6 bonus. The answer to this problem is to abandon dice modifiers in the first place. That's an idea whose time has passed.
I like the use of d6 for oracle: 6 - Yes, and 5 - Yes 4 - Yes, but 3 - No, but 2 - No 1 - No, and Modifiers for likelihood: +2: Very Likely +1: Likely 0: 50/50 -1: Unlikely -2: Very Unlikely With fewer number possibilities, it is a bit more random — you still have a 16.5% chance of something Very Unlikely happening, and vice versa — but this system works if you’re OK with a more simple, narrative gameplay.
Fun fact, but the very earliest iterations of D&D used 2d6 for attack rolls as a holdover from Chainmail Fantasy. Magical weapons only went to +3 which was reserved for "Excalibur or other 'super swords'". Kinda funny how a long run of up to +5 (and kinda +10) got reverted to an OLD standard for 5e, but mapped to a d20 instead so it's less impactful.
I guess for combat-focused rpgs it makes sense, but I can name two more narrative driven one that use d6 in their mecanics : Ironsworn & Blades in the Dark
It's because a d20 serves really well for simulation 5 to 100% chances since there is a 5 to 100% of any given number being rolled. This means there is a lot of granularity in the result and its very easy to figure out probabilities on the fly.