5e Monster Math on a Business Card

TL;DR
For a 1:1 fight of monsters against party, set the Monster Level to the party level; you can use a 2:1 fight with 50% of this number or a 1:2 fight with 150% of it. Then assuming no special abilities, each monster has:

Hit Points: 10+10*ML
AC: 12 + ML/3 (round up, cap 22)
Poor Ability Chk: -2 (flat)
Ability Chk: ML/3 (round up, cap 10)
Damage Per Round: 3.5*ML (or equivalently, d6s)
Attack Bonus/Trained Chk: 2 + ML/3 (round up, cap 12)
Save DC: 10 + ML/3 (round up, cap 20)

Long form:

4e had, in its favor, really quite simple monster math. A monster of level X with the given role and difficulty descriptors should have an AC of X and hp of Y and damage of Z.

5e lacks that. And for how relatively simple the meatbag creatures really are, that’s a shame.

I don’t think you can reasonably expect to back-derive a linear relationship between monster particulars and stats — people have been trying super hard! — but I do think you can come close enough that it’ll work most of the time.

The DMG is, sadly, insufficient to my needs. The chart on page 274 lists “average ranges” (not a super helpful behavior in the first place) and lists hit points which are ludicrously above the ranges used in actual practice. Part of this comes from the monsters tending to be “glass cannons”, with offensive CRs several notches above their defensive CR. Part of this comes from figuring resistances and immunities into their hit points as a multiplier.

Remember: This is only intended to be used for goons! Produced monsters have no real basis in 5e stats!
Per the sly flourish blog post, a hard battle with 1:1 monsters gives those monster half the party’s level in CR (mor or less); you can double your quantity at 50% of the CR or halve it at 150% of the CR. Sly was very careful to keep his stats street legal. For what I’m doing, damn the torpedoes: several levels where things round down (or otherwise keep you from dying horribly) I instead make no such adjustment in the interest of having a clear and simple rule.

I’m introducing a proxy variable so that I have a little more fine-tuned control here, and so that you don’t need to halve everything. Monsters have a Monster Level (ML) equal to the level of the PC they’re 1:1 swapping for. You can put in two ML/2 monsters for a monster of a given ML, or one 1.5*ML monster for two monsters of a given ML.

Then, surfarcher did this analysis on the actual 5e monsters (instead of the DMG table). And one of the sage advice columns talked about converting previous edition monsters into 5e — and in previous editions, monster HD tracked with their notion of monster level pretty closely, so we can also use those proposed adjustments if we squint. Again, ruthlessly simplifying the data and bearing in mind that ML is about twice the CR, we find there are some linear-ish relationships here, at least up until the party is 20th level.

The relevant formulae:
Hit Points: 10+10*ML
AC: 12 + ML/3 (round up, cap 22)
Poor Ability Chk: -2 (flat)
Ability Chk: ML/3 (round up, cap 10)
Damage Per Round: 3.5*ML (or equivalently, d6s)
Attack Bonus/Trained Chk: 2 + ML/3 (round up, cap 12)
Save DC: 10 + ML/3 (round up, cap 20)

I have this ridiculous thing where I consider melee attacks to be “too weak” in D&D — you might consider letting monsters with good ranged attacks under these rules take a -2 AC penalty.
Similarly, this produces fairly high “soldierly” ACs; if your monster is meant to be a brutish monster, consider reducing its AC by 2 and increasing its attack by 2.

I divide ML by 3 even though the wizards article used HD/2 because IMO they get it wrong 🙂 Originally I too used HD/2, but then my hit points seem ludicrously out of whack; adjusting that to /4 felt too low so I wanted to add a tier modifier. 1/3 feels just right and tracks with a few quick sanity checks:

Under these quickie rules, an Ogre (CR2=ML4 or 5) is
HP: 50 or 60
AC: 14
Atk: +4
Chk: +2 (such as its constitution save…)
DPR: 14 or 17
That seems awfully close to the real thing — the AC and damage values are a tiny bit high, but the attack bonus is a bit low; if you gave it -2 AC and +2 attack (which seems like a fair brute-style modification), I think I could use that and be the only one at the table to realize what I’d done.

Similarly, the bag-of-meat Hill Giant (CR5=ML10 or 11) is
HP:110 or 120
AC: 16
Atk: +6
Chk: +4 (such as its constitution save…)
DPR: 35 or 38
Again, right on point (ed: note it splits its DPR between two attacks)! We can see it has the same ogre-style -2 AC/+2 attack bonus brute-style stat swap.

These rules don’t cover, nor do they reserve space for, special features; they just give a flat reasonable value for an averageish monster at this ML. These hit point numbers are significantly higher than those in the MM, so if you do want to throw RELEVANT defensive features on a monster (ed: like incorporeality at low levels, flight and ranged attacks at mid levels), consider using a variant of the table on DMG 277 to modify the monster hp to keep it fair. If the abilities you’re using don’t seem like a big hindrance to the party (for instance, just fire resistance and nothing else) feel free to skip this. Adjusting that table’s CR for my ML, we get:
ML 1-8: 1/2 the monster’s HP
ML 9-20: 2/3 the monster’s HP
ML 21-32: 4/5 the monster’s HP; note flight in particular is no longer considered a defensive ability
ML 33+: You’d have to get pretty cray cray to care.

Similarly, these assume damage is flat and distributed to a single target. Start doing weird things like “multitarget attacks” and you should modify the expected damage as above.

That’s it!

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About lackhand

I was born in 1984 and am still playing games, programming computers, and living in New York City. View all posts by lackhand

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