How do you determine hit points in 5e for custom monsters?

Before anyone says it, I did look in the DMG. The table listed there is, as far as I'm concerned, completely useless if one's starting from a certain CR. The hit points column puts down a range of hit points that's way above the range I see in actual monsters of the listed CR in the MM. CR 1 has its hit point range as 71-85, but not a single monster I'm seeing has hit points in that range. So how do I determine hit points? What are the rules for it? How does CR correlate to hit points if the table doesn't list that?

• Hmm, you read the rules on this, and you didn't like them. But now you're asking where the rules are. You have a good point about the hit point range, and I think there's a good question here, but there is no secret "other rules" for this. – Tim Grant Jul 14 '16 at 0:26
• @timster To be fair, the table does seem to be straight-up wrong, or at least entirely unrelated to any published monster's HP. Doubting its utility seems natural after comparing it to a few randomly selected monsters, not a matter of merely not liking it. – SevenSidedDie Jul 14 '16 at 0:33
• Did you scale up the randomly picked CR1 creature's HP by the AC it has? Did you take into account its Offensive CR? Remember the final CR is a combination of both Offensive and Defensive CR. Also, the monster's abilities have a large impact. See: Goblin's Challenge Rating and Nimble Escape, Ogre CR calculation: is it wrong or am I missing something?, Reverse engineering the Hydra CR – daze413 Jul 14 '16 at 2:08
• Related reading: monster building 101, 201, 202 by AngryGM. Be warned of rude language interspersed with excellent advice. – nitsua60 Jul 14 '16 at 3:04
• I think daze413, nitsua60, and Ilya Donskikh pretty effective answered my question...I think that satisfies me. – MisterGunpowder Jul 14 '16 at 3:34

Give it levels in a class for the purpose of determining hit dice.

This can also be raised up to whatever maximum of levels you need, and the hit dice can also be whatever makes sense. The highest monster in the MM is the Tarrasque with 30d20 hit points, and 30 Constitution.

Or... calculate the average amount of damage your party deals per turn, and scale the difficulty based on how many rounds you want the combat to last.

The longer the combat, the harder it is for the adventurers to fight. Say that given all attacks hit (calculating AC is outside the scope of this question), your adventurer party deal a given amount of damage a round on average in total. You would multiply said given amount of damage by how long you want the encounter to last in rounds (based on your party's total hit points and how many hit points of damage your monster deals on average given it hits). If you want to even more accurately do this, calculate the probability both the party and the monster hit their attacks given their average AC.

Or... make it up, and using trial and error see what works and what doesn't.

Do make sure not to slaughter the party if you decide to take this approach.

As for the last part of your question... the Challenge Rating has no direct correlation to hitpoints. Rather, it is a combination of features of the monster including hit points, AC etc. For example, a monster could be fairly weak by first looking at just its AC, hitpoints and damage, but it could have other features which make it very difficult to fight.

• "the Challenge Rating has no direct correlation to hitpoints. Rather, it is a combination of features of the monster including hit points..." - isn't that kind of the definition of correlation? – Olorin Jul 15 '16 at 8:45
• For the sake of this, when I said direct I meant 'sole impact'. I meant that there is a lot more than just the hit points, damage etc. If you can phrase it better, please edit the answer to be clearer for future use. – Ilya Donskikh Jul 16 '16 at 12:35