How to set DCs.

[frogglesmash]

Basically what the title says. How do you guys go about setting DCs for skill checks and saves without having them be arbitrarily high or low depending on if you want the PCs to succeed or fail?

[Chronos]

First of all, you don't decide whether you want the PCs to succeed or fail. You need to make sure there's some way through the adventure you've set them, but that way doesn't necessarily need to be the way you intended, and you can have potential paths available which are too difficult for them. I think that's what you were already saying, but I just wanted to be clear.

OK, then. If it's a simple task that an average person could succeed at about half the time, that's DC 10 (strictly speaking, it should be 11, but it's always rounded to 10). Something that you can imagine some ordinary folks doing routinely, but which not everyone can do consistently, is 15. If it's the sort of thing you'd expect to have some specialized training in before doing it, 20. 30 is for the sorts of things routinely done by people at the top end of their skill level worldwide, and 40 is somewhere between world-record performance and "I think someone might have done that once, ever". Beyond that, unless there's some obvious way to extrapolate the numbers (the lower-DC tasks fit some simple formula), you're just talking about "humanly impossible", and just how humanly impossible you want to make it is largely arbitrary.

[frogglesmash]

First of all, you don't decide whether you want the PCs to succeed or fail. You need to make sure there's some way through the adventure you've set them, but that way doesn't necessarily need to be the way you intended, and you can have potential paths available which are too difficult for them. I think that's what you were already saying, but I just wanted to be clear.

Yes, that's what I was saying, I'm trying to get feel of how to set DC's in an objective manner, and I think your advice covered it quite well.

[NevinPL]

Most DC are set, or acquired by provided formula.
The "default" DC is 15.
DMG says about the +/-2 modifier to use when needed, and has about 4/5 of page of DC examples.
If you remember about "take 10" rule you got nice "borders" for coming up with your own DC's.