D&D 5E Challenge Rating formula...

[cthulhu42]

For the life of me I cannot find a CR formula for figuring out how many multiple monsters equal a given CR.

In other words, what would be the CR of an encounter with three CR5 foes?

How about a CR8, CR6 and a CR 4 creature?

If I have a party of 4 6th level PC's, how many CR2 monsters do I throw at them to equal a CR6 encounter?

 

[I'm A Banana]

DMG pg. 82.

Also available in the Basic DM doc, IIRC.

 

[Cernor]

Using CR as a metric for encounter difficulty is a thing of the past. In 5e it's based around the XP each monster gives rather than what CR they are... So CR by itself is only really useful to determine if what you're throwing at your party is likely to be way too difficult (using a CR 10 monster with 3rd-level PCs, for example).

 

[ExploderWizard]

Using CR as a metric for encounter difficulty is a thing of the past. In 5e it's based around the XP each monster gives rather than what CR they are... So CR by itself is only really useful to determine if what you're throwing at your party is likely to be way too difficult (using a CR 10 monster with 3rd-level PCs, for example).

This is a good benchmark but there are other factors in play as well. A given XP total might be overwhelming for a party on paper, but if the encounter is done in at least two waves, the same XP total could be workable. Even without a rest, not having as many foes to deal with at once makes a huge difference.

 

[Tormyr]

What you are actually looking for is encounter building. Encounters are generally looked at as Easy, Medium, Hard, or Deadly. CR of a creature determines the XP value for the creature, but the XP value and multipliers determine the XP difficulty for the encounter. This is different than the XP awarded to the party.

To simulate encounter CR/Encounter Level, make a Medium encounter for a group of PCs of the same level as the Encounter Level you are looking for. This can be different than the level of the party. For your examples, assuming 4 PCs:
3 CR 5 monsters: Encounter XP 10800, awarded XP 5400, a medium encounter for a level 12 party so it could be considered as EL 12, a potentially Deadly encounter for parties of level 9 and below.
3 CR 8 monsters: EL 17
3 CR 6 monsters: EL 14
3 CR 4 monsters: EL 10

3 CR 2 monsters would be a Medium encounter for a 6th level party of 4.

Medium encounters are expected to use some party resources and have a low chance of lethality.

You can use my encounter building spreadsheet to quickly calculate encounter xp.

http://www.enworld.org/forum/rpgdownloads.php?do=download&downloadid=1186

 

[fjw70]

I suggest this alternate encounter building system just using CR.

http://slyflourish.com/5e_encounter_building.html

 

[Mistwell]

I suggest this alternate encounter building system just using CR.

http://slyflourish.com/5e_encounter_building.html

I find that list comes up with MUCH easier challenges than the existing system.

I find this tool really useful.

 

[fjw70]

I find that list comes up with MUCH easier challenges than the existing system.

I find this tool really useful.

Then bump the numbers up a step or two until it works for you. I much prefer a simple rule of thumb I can do in my head to using a website, but to each his own.

 

[Mistwell]

Then bump the numbers up a step or two until it works for you. I much prefer a simple rule of thumb I can do in my head to using a website, but to each his own.

How about "it doesn't even vaguely match the 5e guidelines" as an objection? I mean, just work it out in some samples - that system doesn't even come vaguely close. in fact it almost seems like it comes up with D&D Next playtest type results rather than 5e-based results.

 

[Elric]

DMG pg. 82.

Also available in the Basic DM doc, IIRC.

The original encounter design guidelines are flawed and overstate encounter difficulty when you have monsters at very different CRs (and the "XP multipler" is a clunky concept that makes designing encounters difficult). I haven't looked at the update to the DM Basic Guide from November in detail, but it looks much the same (I presume the DMG is similar).

I recommend Gobelure's thread on how to modify the encounter design guidelines to fix this problem, so that you don't need an "encounter XP multiplier." http://www.enworld.org/forum/showthread.php?367697-Encounter-difficulty-how-to-fix-it The key is that in Gobelure's new tables PC and monster power scales more slowly with CR/levels, so that you don't need the "fudge factor" of the "encounter XP multiplier."

Here's how I described the issue in that thread:

It seems to me that PC and monster power doesn't scale as fast in general as the XP numbers alone would imply (e.g., a CR 5 Hill Giant worth 1,800 XP is not as deadly as 4 CR 2 Ogres worth 450 XP each). So large numbers of lower CR monsters would be too strong relative to what the XP total suggests.

The encounter XP multiplier (basic DM guide, p. 57) helps to address that design flaw. However, the XP multiplier is itself flawed (as an encounter with an Adult Red Dragon and 3 Kobolds demonstrates).

My take is that some monsters are particularly dangerous in groups (e.g., with their own kind, like Intellect Devourers, or with any melee combatant, like Hobgoblins). Those should have been handled with special guidelines in their stat blocks (CR varies based on group composition), and XP should have simply scaled more slowly as CR increased (with the corresponding decrease in the XP budget encounter guidelines), thus obviating the need for a multiplier.