Balancing CR vs. Party Size

[Chrismith]

A simple question: I know that monster CRs are balanced for a four-character party. How would the party ECL be affected by more or fewer characters? For instance, if a CR 10 monster is an appropriate challenge for a party of for 10th level characters, what CR would be a good match for a single 10th level character? Or six 10th level characters?

I know I've seen this info somewhere before (in the DMG, I would assume) but I can't seem to find it at the moment.

[Worira]

Page 48-49, I believe, but this (http://www.penpaperpixel.org/tools/d20encountercalculator.htm) works pretty well. Just keep in mind that CR is more of a guideline than a rule: some parties can take on a higher CR, some can't.