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I noticed how D&D 5e's Hexblade Warlock subclass feature Armor of Hexes imposes a chance to miss regardless of the attacker's roll. That chance is based on a d6: if it's a 4 or higher it misses, and anything else it hits if the attack should have hit. To my understanding, this is simply a 50/50 roll on the d6 (success on 4, 5, 6, failure on 1, 2 and 3).

Out of curiousity, does it matter if the dice is a d4, d8, or even d100, as long as it's an even-sided die and that it's still 50/50? (On a d4 it would be a success on a 3 and 4, on a d10 it's 6 and up, and so on.)

Eddymage
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field158
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3 Answers3

37

Mathematically speaking, it does not matter. You could even use an odd-sided die and reroll on one specific outcome, e.g. the lowest one.

The reason for choosing a d6 in the rules could be that it's the most common die. It's also arguably the easiest die to read off the result of the roll.

Glorfindel
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    Not really a game-breaker, but the guess towards designer intent probably doesn't really belong in the answer. – NotArch Jan 10 '21 at 17:05
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    Is there a possibility of a modifier (or advantage/disadvantage) being applied? Might change the answer. – Joshua Jan 10 '21 at 18:52
  • From a ComSci standpoint, does having a wider range of numbers for it to be 50/50 matter? Aka if you generate a random between 1-100 vs random between 1-2 or 1-6? Is one more likely to be more 'random' or 'fair'? – cclloyd Jan 10 '21 at 23:30
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    @cclloyd No, it's the same story. Computers generate random number "ranges" by adding and multiplying the number generated by whatever algorithm you've used, so there's no meaningful difference between multiplying your random number by x to get 1-2 or by 2x to get 1-4. – Alex F Jan 11 '21 at 00:50
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    Taking an odd die size does have the risk of spending the rest of eternity rerolling and constantly rolling the lowest one. Though, since you are not a robot you would probably notice in due time that you are wasting time and go get a d6 – Poseidaan Jan 11 '21 at 16:35
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No, it doesn’t matter.

There isn’t really much to say here. As long as you have the same number of even and odd faces on the die, there will be no difference (assuming a fair die).

Again, this assumes a fair die. The only way to know if your die are appropriately fair is to test them by rolling them and recording the results.

Thomas Markov
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  • @Medix2 I don’t understand, but that may be because of my lack of knowledge of systems beyond d&d 5e. – Thomas Markov Jan 10 '21 at 14:36
  • @Medix2 how do you mean? Like attack roll modifiers? – field158 Jan 10 '21 at 14:36
  • @Medix2 I still don’t understand. – Thomas Markov Jan 10 '21 at 15:03
  • I think Medix2 is saying that if a roll isn't a straight 50/50 chance as described by OP, but instead includes modifiers, then the die number actually would matter. But I'm not seeing that's OP's case, so I'm confused as well. – NotArch Jan 10 '21 at 15:03
  • Right but games that use modifiers like that will explicitly prescribe a die size. 50/50 is 50/50. – Thomas Markov Jan 10 '21 at 15:09
  • @Medix2 I'm pretty sure there aren't any features (in the D&D 5e context it is asking about) which can affect any dice roll, it would do weird things with various features. – Someone_Evil Jan 10 '21 at 15:09
  • Also what DM is going to allow you to game the system by arbitrarily changing die size? In any system, it will be entirely unambiguous when a feature requires a certain die size. – Thomas Markov Jan 10 '21 at 15:11
  • @ThomasMarkov The OP describes the rules as calling for a d6, with 4,5,6 as success and then asks if it's really necessary to use a d6, or if some other size die would suffice. So it seems like that's the crux of the matter! – user3067860 Jan 11 '21 at 19:05
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Does not matter for result, matters for convenience

50/50% will be, mathematically, the same no matter the die. So let's see what we got to choose from:

  • d4 rolls poorly. Actually, it hardly rolls at all
  • d6 rolls pretty OK and there is a high chance people have some to spare, from other games or for Fireballs
  • d8 & d10 rolls poorer than d6, although your mileage may vary
  • d12 tends to be lost as it is rarely used
  • d20 is the one attacker uses, so if there is only one set of dice per table, as some tables have, it is not readily available.

This leaves d6 as an usually most convenient die to roll half-half checks.

Mołot
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    While your experience is more than welcome to support an answer, judgements on what dice people like to roll and perceived issues are going to be totally opinion-based. – NotArch Jan 10 '21 at 17:10
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    @NautArch This looks like an experienced based answer to me, since the experience he has shared looks a whole lot like the experiences I've come across in re how the die sizes work ... though I go out of my way to use a d12 when I can (just a personal thing) – KorvinStarmast Jan 10 '21 at 23:38
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    I find it strange that you omitted d2 (AKA coin) from your list of options. Most tables do have d2 available, even if they don't use them. – Brian Jan 11 '21 at 14:19
  • @Brian Coins aren't perfectly fair, though – Punintended Jan 11 '21 at 20:47
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    @Punintended neither are most of our dice :) – NotArch Jan 11 '21 at 21:34
  • @NautArch Nonsense! As you can see by this cross-section, my dice are perfectly fair >.> – Punintended Jan 11 '21 at 22:04
  • Just as a side note - in my experience, d20 can sometimes be hard to read. Depends on how far away you roll it - e.g., whether it's in front of you or towards the middle of the table. If it's further, you see it at an angle and it's harder to make out what value is on top because there are four of them in close proximity.. A d6, for example, is unambiguous at any distance where you can make out the numbers. – VLAZ Jan 12 '21 at 06:48