When aiming to roll for a 50/50, does the die size matter?

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.)

• "No, they do not yield the same probabilities" because "it is not a fair die." – When rolling percentages, do 1d100 and two d10s (percentiles) share the same probabilities? Commented Jan 11, 2021 at 0:52
• For 50-50 stuff, some Pokemon Coins are surprisingly readable even from far away. I can't recommend them enough if you need any sort of coin-toss or similar for any RPG game. Commented Jan 12, 2021 at 21:52

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.

• Not really a game-breaker, but the guess towards designer intent probably doesn't really belong in the answer. Commented Jan 10, 2021 at 17:05
• Is there a possibility of a modifier (or advantage/disadvantage) being applied? Might change the answer. Commented Jan 10, 2021 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'? Commented Jan 10, 2021 at 23:30
• @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. Commented Jan 11, 2021 at 0:50
• 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 Commented Jan 11, 2021 at 16:35

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.

• @Medix2 I don’t understand, but that may be because of my lack of knowledge of systems beyond d&d 5e. Commented Jan 10, 2021 at 14:36
• @Medix2 how do you mean? Like attack roll modifiers? Commented Jan 10, 2021 at 14:36
• @Medix2 I still don’t understand. Commented Jan 10, 2021 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. Commented Jan 10, 2021 at 15:03
• Right but games that use modifiers like that will explicitly prescribe a die size. 50/50 is 50/50. Commented Jan 10, 2021 at 15:09

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.

• 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. Commented Jan 10, 2021 at 17:10
• @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) Commented Jan 10, 2021 at 23:38
• 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. Commented Jan 11, 2021 at 14:19
• @Brian Coins aren't perfectly fair, though Commented Jan 11, 2021 at 20:47
• @Punintended neither are most of our dice :) Commented Jan 11, 2021 at 21:34