quick question

[Rahdjan]

What's the difference between a CR and ECL?

[Innis Cabal]

one a difficulty and the other is how powerful a race/template is and how it effects your level. Like vampire is ECL+8 that means if you are level one and you become a vampire you level as a level 9 character

[Rahdjan]

gotcha and thanks.

[Douglas]

CR is a measure of how powerful something is in a single combat against a typical adventuring party. ECL is a measure of how powerful something is over the course of a whole adventure or campaign as part of an adventuring party. CR is typically much lower than ECL, at least in part because the single combat won't last long enough for the creature to make full use of all of its abilities (this is especially true for creatures with at will abilities), but also because many abilities or bonuses that aren't all that powerful for the base creature synergize well with well chosen class levels.

[Zincorium]

CR is a an NPC only concern. ECL is a PC only concern. Don't attempt to use one to figure out the other, there is no equivalence because of the way they're used.

CR is all about how much of a challenge something should pose and how much experience and treasure should result.

ECL is a means by which you can play odd or powerful characters and still have them in around the same power category as the rest of the group (although this doesn't hold up all that well at the extreme ends). Your character level is your class levels + your monster hit dice (if any), which is used to determine feats, ability score increases, and skill maximums, as well as when you become epic. Your effective character level is your character plus your level adjustment, and doesn't determine anything except how much xp you need.

[kamikasei]

one a difficulty and the other is how powerful a race/template is and how it effects your level. Like vampire is ECL+8 that means if you are level one and you become a vampire you level as a level 9 character

This isn't quite right. There's no such thing as "ECL+8", there's a character with one class level and a +8 Level Adjustment, which adds up to make a character with Effective Character Level 9.