Appropriate CRs for party sizes other than 4

[ken-do-nim]

I'm trying to come up with a way to figure out what the appropriate challenge rating is for party sizes other than 4. Do you think it's -1 to the CR for each character < 4 and +1 to the CR for each additional? Is it -25% of the CR for each character missing and +25% to the CR for each additional? Is there a different formula at low levels than mid than high?

In particular, I'm trying to get a friend to DM my level 17 sorcerer and my other friend's level 16 barbarian next month, and I'm not sure what level adventure he should prepare. What if my other friend can't make it and my sorcerer goes solo? What if we get one more person to play?

[Thomas]

First, don't think CRs. Think ELs.

Basically, it should be proportionate to the experience. If you've got two guys, they're getting twice the experience from the same amount of encounters, so you drop EL accordingly. (Instead of a CR 6 monster, they meet a CR 4 monster; instead of two CR 5s, they meet one CR 5 or two CR 3).

I don't have my DMG at hand, so I don't recall off-hand what the EL drop is, but I should think it's two, too. Check out the EL ratio table (15% of party level +1, etc.), and take 2 off each EL, then go with that.

Ultimately, as always with CRs and ELs, it's an art. You need instinct. An experienced GM knows what the PCs can handle, and with how much trouble. (How else could we run games with no silly CR systems, eh?)


Edit: For varying party sizes (I get a lot of that), I often design encounters at several ELs for various numbers of PCs. I always have enough monsters that the same encounter yields the same XP per PC, no matter how many PCs.

[Mike_G]

For a smaller group, it depends which roles aren't being represented. You need to look at a party with no arcane caster differently than one with no rogue.

I often would design encounters for a variable party size. For instance, a low level encounter with goblins might include a goblin leader with a few levels in warrior, a shaman and three normal goblin warriors per PC.

[NullAshton]

http://www.d20srd.org/encounterCalculator.htm

All you really need. Just put your characters in on the right, the monsters in on the left, and it automatically tells you XP, difficulty of the encounter, average treasure value of the encounter, and other fun stuff.

[Wayloss]

the calculator is way off on the difficulty aspect.....

[paigeoliver]

For five characters CR is still same. For 6 characters it is one higher. That is the same math the EL system uses if you have a group of 4 monsters, then add 1, then add another 1.

I would subtract one for each character under 4.

[ken-do-nim]

thanks everybody

[silvermesh]

systems and formulae aside, you really do have to just sit down and play an adventure or two before you can really decide what challenges are good for your PCs.

I mistakenly threw a couple ogre zombies at a group of level ones before, and what could have easily been a TPK with any other group, my players made it through on wit and cunning.