3.5 Challenge Ratings Question?

[Mojake]

Since a party of four Level 3 PCs is a level 3 party; does that mean that if a creature has a CR of 3, you need four of them to have an equal fight?

This has confused for a while now.

Thanks.

[hamishspence]

For them to be an equal match up with 50/50 chance of winning, yes.

In practice four of the same creature may be weaker than four creatures with different, very complementary abilities.

[Yora]

No, the theory is that you have one CR 3 creature for four level 3 characters.

And yes, a single 3rd level human is considered a good encounter for four 3rd level characters.

By default, the average encounter should be something that has the PCs do some work, but something they should win without serious problems.
PCs are expected to have so many fights, that most of them will be a pretty safe thing for the PCs. If every fight was a 50/50 chance to win, the PCs would be unlikely to survive more than a small handful rather than the more than 200 it takes to reach 20th level.

However, the CR of any creature is always just a rough estimate that does not take into account the specific abilities and equipment the group might have. A pack of werewolves would be much easier for a group of characters who all have silver weapons than for a group in which nobody has a silver weapon. When preparing an encounter for a group of characters, you always also have to check that the PCs have weapons and defenses with which they can harm the monster or defend themselves against it.
A shadow is only CR 2, but a single shadow against a group of 2nd level characters without magic weapons can kill all of them without problem.

[hamishspence]

True- but the OP asked about what would be an "equal fight".

Which can make a good final encounter for an adventure.

[Urpriest]

The important point here is that, except for the occasional high-stakes situation, you don't put your PCs through "equal fights".

On an average day the PCs are supposed to go through four encounters. If each of these was an "equal fight", with a 50/50 chance for either side, the PCs would only have a 6.25% chance to survive the day.

Instead, most fights are unequal: for a third level party, one monster of CR 3, or a group of monsters with EL 3 (if you don't know what EL is, you should read up on Encounter Level, it's the basic principle behind encounter design as outlined in the DMG). This means you can have four fights a day and only be at risk of dying on the last one, because each fight uses up roughly 1/4 of the party's resources.

Now occasionally you'll throw a true "equal fight" at the PCs. But those should be rare and dramatic occasions, generally with lots of foreshadowing and preparation.