D20, Divinities, and why Nuking Makes Me Thor

Today we have a question…

How much damage does a d20 nuke do? Will it kill a d20 god?

Now nuclear weapons really are pretty impressive. They’re by far the most powerful weapons yet developed by human beings. Of course, d20 characters… are really not very human. The basic problem here is that, all intuition to the contrary, “damage” in d20 is not linear.

Lets take a standard d20 heavy mace: sized for a 5’6 human being. It does 1d8 damage and weighs 8 pounds. Well and good.

Now lets make it a colossal mace, for a (minimal) colossal creature twelve times that size – 66 feet tall. That’s twelve times as big in each dimension, giving it a weight of 13,824 pounds – and it has to be swung around at twelve times the speed of the basic mace, since it gets swung around in the same way and hits at the same frequency while having twelve times as far to travel.

Kinetic energy is what does the damage when a mace hits – it gets expended crushing flesh and bone, tearing tissues, and otherwise doing unpleasant work on the victim – and our colossal mace carries (12 x 12 x 12) times the mass x (12 x 12, velocity squared) times as much energy as the basic one. All of that energy can get expended on some poor character when it comes down on his head, since being hit will not move a d20 character an inch. So… our Colossal Mace can deliver 248,832 times as much kinetic energy to the target as a normal mace.


That makes some sense; If I get several tons of steel moving at high speed coming down on ME, I must either get out of the way or be turned into a puddle of goo.

Yet the rules tell us that our colossal mace only does 6d6 damage. An average of (21 / 4.5) = 4.67 times as much as a normal one. That’s a damage adder of (+3.5). Still ouch, but certainly not nearly two hundred and fifty thousand times as much ouch. It’s not even enough damage to bother most mid-level characters all that much.

Like it or not, neither hit points nor damage are linear things in d20. They’re logarithmic.

So we’ll be generous on behalf of damage and take the simple calculation; each factor-of-ten increase in the delivered energy equates to a +1 damage multiplier. That would give our colossal mace a damage rating of 6d8+2, but that’s close enough to what the rules give to pass.

According to the d20 (Modern) rules, a standard, roughly half-pound, stick of dynamite does 2d6 damage. Dynamite is actually about 25% more powerful than TNT, but – in d20 terms – this makes very little difference. For our purposes, we can treat them as being pretty much equivalent.

There are special rules in the d20 modern SRD for small bundles of dynamite – giving it a maximum damage of 10d6 and a maximum radius of 20 feet (exactly like a standard fireball) no matter how much dynamite you use, but we’re interested in very large quantities, so we can just extrapolate this calculation instead.

  • One ton of dynamite (4000 times as much, for a +3.6 damage multiplier, rounded to +4) will thus cause 10d6 damage – albeit in a considerable radius.
  • One kiloton of dynamite (4,000,000 times as much, for a +6.6 Damage Multiplier, which I will gratuitously not round off so as to get an easy result. gets us 15d6 damage – albeit with effects spread out over a VERY wide radius.
  • One megaton of dynamite (4,000,000,000 times as much) will, of course, get us up to a +9.6 damage multiplier – and either 20d6 (for easy steps) or 21d6 (for more accuracy) damage – and an immense area of effect.
  • The Tsar Bomba – we’ll be generous and call it an even sixty megatons – gets a multiplier of +11.3 – giving us a figure of 25d6 damage – equivalent to the direct damage that can be caused by a ninth level spell, albeit over a far larger area. Yes, that’s a coincidence – but it’s an interesting one isn’t it?

We can get pretty much the same results by applying the weapon damage chart to small/medium/large/etc explosions – which makes some sense; these are just bigger weapons after all.

Now we’re certainly justified in adding some special effects – perhaps a fortitude save to resist radiation sickness (not that d20 characters have anything equating to “genes” to be damaged since they can have kids with ghosts and creatures who don’t even have material bodies), another to evade blindness (not that sight in d20 necessarily has anything to do with having eyes), yet another to avoid deafness, a knockdown/back effect, and more. We could add a reflex save (to represent being behind cover, which will help considerably) and double the base damage to compensate (although this raises the possibility of characters saving for no damage) – but we’ve got a good lower bound for the use of nuclear weapons in d20.

And, in general… nuclear weapons will not kill a standard d20 god, or most high-level characters, even barring the use of evasive spells, immunities, and other special defenses.

Of course, what we’ve really demonstrated that the d20 mechanics are not that consistent, reliable, or rational – and get worse as you start getting away from the baseline medieval muscle powered weaponry it was designed to work with. After all, the d20 mechanics describe a world where characters can wade through lava up to their armpits and take a mere 2d6 damage – which remains the same as long as at least one finger is sticking out. Now, if you want a plot device, you can go ahead and give your weaponry completely arbitrary effects. If you want something that’s more or less playable, there’s a rather long list of absurdly overpowered weaponry over here – most of which does fit these calculations fairly well.

4 Responses

  1. […] damage is not linear. For example, as explored HERE, a medium size Mace in d20 hits for 1d8 damage plus strength modifiers – often enough (with […]

  2. […] making hit points utterly abstract and damage non-linear. A hit from a Colossal Mace should – by virtue of basic physics – be capable of doing hundreds of thousands of times as much damage as a hit from a 1d8 […]

  3. […] those wanting modern or exotic weapons, here are discussions of Modern Weapons in D20 and Exotic […]

  4. […] d20 damage rules are not linear however, which is why a direct hit with a one megaton fusion weapon only does 16d8 damage and why a hit […]

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