Kubular & Other Attack Methods

Occasionally, I check Reddit to see if I missed anything interested in this sphere of things. Not usually, but today—yeah! Reddit user Kubular reported a misunderstanding of typical D&D combat from one of their friends, and took it as a possible new direction for one-roll combat. Here’s the link, and here’s the important bit:

I rolled a 16 to hit and they had an AC of 13. I rolled a 5 for damage, but she was still looking at the 16 and was like “wait, why is it 5? Shouldn’t it be 3?” I was confused for a moment, but then I realized (a) she hadn’t seen my damage roll, and (b) I hadn’t explained how combat works and this was her first exposure to any RPG. So she saw the 16, understood armor class as representative of her armor, then just assumed that you would subtract the AC from the attack roll to get damage.

Math Comparison

That’s interesting! How does it compare to other methods? Let’s take for example:

  • Original: Attempt an attack as per Chainmail, and take 1d6 damage upon a hit.
  • Classic: Roll d20 to attempt an attack, and take 1d6 damage upon a hit.
  • Oddlike: Roll 1d6 and subtract armor.
  • Kubular: Roll d20 and subtract armor class.

For each, I’m going to assume four armor types: none, light, medium, and heavy. These may not necessarily translate 1:1 between these different systems, but they’re close enough.

Armor Types & Corresponding Values

Armor Original Classic Oddlike Kubular
None 7 10 –0 10
Light 8 12 –1 12
Medium 9 14 –2 14
Heavy 10 16 –3 16

And here’s the results:

Damage Points per Attack (DPA)

Armor Original Classic Oddlike Kubular
None 2.04 1.93 3.50 2.75
Light 1.46 1.57 2.50 1.80
Medium 0.97 1.22 1.67 1.05
Heavy 0.58 0.88 1.00 0.50

As expected, the Oddlike deals overall more damage than the other three; I mostly wanted to include it for comparison. The Kubular method is interesting in that unarmored characters suffer more than via the Original or Classic methods, almost by 40%, but armored characters are relatively as protected as they would be via the Original methods. This is because the damage dealt depends on the result of the attack roll, rather than being separate and arbitrary with respect to it. It’s 2d6 results with a 1d20 roll.

Let’s represent each row as a % of the no-armor result.

DPA, Relative to No-Armor

Armor Original Classic Oddlike Kubular
None 100% 100% 100% 100%
Light 72% 81% 71% 65%
Medium 48% 63% 48% 38%
Heavy 28% 46% 28% 18%

Isn’t it crazy that the Oddlike method is proportionally so similar to the Original method, except that the raw numbers are bigger?! Let’s invert it for fun, too, since that helps us understand how much “better” armor is:

Inverted DPA, Relative to No-Armor

Armor Original Classic Oddlike Kubular
None 100% 100% 100% 100%
Light 139% 123% 141% 153%
Medium 208% 159% 208% 263%
Heavy 357% 217% 357% 555%

Then, let’s set that relative to the Classic method (1.93 damage per attack), using the non-inverted results so we see how effective attacks are.

DPA, Relative to Classic No-Armor

Armor Original Classic Oddlike Kubular
None 106% 100% 181% 142%
Light 76% 81% 129% 92%
Medium 51% 63% 87% 54%
Heavy 29% 46% 50% 25%

This means that the Kubular method is overall 42% more effective against unarmored opponents, but 45% less effective against fully armored opponents. Whether that’s a good or bad thing is entirely subjective.

Refining the Method

People pointed out in the comments that having to do subtraction to find out how much damage you deal is kinda annoying, but there’s an easy fix. If there ever was a time for roll-under resolution, this is it. You could use straight-up descending AC, but that feels a little more punishing and doesn’t actually match the stats above. Thankfully, instead of that, we can use nicer-looking even numbers.

Armor Old AC New AC Chance
None 10 10 50%
Light 12 8 40%
Medium 14 6 30%
Heavy 16 4 20%

This method is very straightforward. The armor number tells you, at least as a basis, the maximum damage you can take from being attacked. Roll d20 less than or equal to the new armor class, and if you succeed then the result is how many points of damage the target takes.

It even scales really nicely with attack bonuses, which you just slap on top. If a level-4 fighter increases their combat capability by 1 per level, then they roll against 14 for an unarmored target or 8 for a fully armored one. If the maximum hit dice a monster can have is 10, which tends to be the convention (as much as I may prefer binary powers), then that translates to dealing anywhere from 1 to 20 points of damage against an unarmored target. Scary!

Hit Point Refactoring

Is there a super big worry about hit points needing to be adjusted? Actually, I don’t think so. There’s a scheme I have in FMC Basic that I refer to above, that uses binary powers to distinguish between brackets of monsters based on the idea that there are 4 hit points per hit die. Please let me know if you have better ideas for naming conventions; I don’t like “lieutenant”.

Bracket Hit Dice Hit Points ATK
Mook 1/2 2 1
Grunt 1 4 2
Elite 2 8 4
Lieutenant 4 16 8
Boss 8 32 16

Since this already gives a slight buff to hit points, I kinda like it. The 8 HD boss is just 3 hit points away from the average 10 HD monster using d6 for hit dice. It also makes it really easy to calculate, at least for early level characters, how many attacks it will take to down a monster of that bracket given their armor or defense class. The ATK column assumes a light defense class; multiply it by 2 for medium defense, or by 4 for heavy defense.


Will I switch to the Kubular method? Can't say; I play games more often than I run them. I think it's interesting, and it used to be how I wanted to do attack rolls in my demon catching game that didn't go anywhere before I got stuck on FMC. Maybe I would try it!


  1. I love seeing folks do math to OSR games like this! It makes me feel less silly about my own OSR-math noodlings, but more importantly, it's cool to see what other people have discovered. (I recently discovered your blog and am riding the high of binge-reading)

    The Oddlike method being proportionally similar to the Original, but with bigger numbers makes a lot of sense to me. While most Oddlikes give PCs a small pool of hit points, damage often 'overflows' into a larger pool of harder-to-recover hit/ability score points. I also think the refined method is super elegant! Most roll-under systems with level-based modifiers often end up with weird subtractions, but this maintains the simplicity of roll-under while making it so you only have to add.

    I'm confused by what the ATK in the hit point refactoring is supposed to be. Is that supposed to be how much you add to the PC's AC/damage upper bound?

    1. thank you!! and ATK stands for "attacks to kill", it's just how many attempted attacks it takes to defeat a figure of that bracket :)


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