Re: About the calculator
Kalendraf said:
I entered the party (1x8, 3x9, 2x10) and the effective party level shows 10.4
I next entered the critters in the tomb (3 gargoyles plus 6 lizard-wights = 9 CR4 cretures) and the effective encounter level shows 10.3
The comment shows "Challenging" and advice of "Keep on your toes".
The moral here is that there are cases where it just doesn't easily boil down to a simple formula.
There is a large problem with the CRs and how they work out. Upper_Krust and others have done quite a bit of work on this. It is generally observed (and WotC admits this) that dragons deserve significantly higher CRs - generally 2-6.
If you are reasonably confidant that a given CR for an individual creature is accurate, you can measure just how much outnumbering plays a role by squaring the outnumbering factor involved, IE
Your party was outnumbered 1.5 to 1 (9 to 6), so squaring the factor gives 2.25. By WotC's claim of how CR works, this would be CR +2.25, or CR 6-7ish (say for beefy CR 4 or good tactics/situation)
Which results in about 750 XP for your party to split for that encounter.
This still assumes that CRs for individual creatures are accurate, and double power = CR+2.
When numbers besides 4 are involved, you need to factor in the numbers of your party as well (6 people versus 9 is a lot different than 4 versus 9, that would be 2.25^2, or +5 = CR 9, two extra party members drops CR by 3!)
An easier way to think of how this works, take three fighters, level 1, identicle hit points, etc. Now have them fight 2-on-1. Watch them maul the 1 fighter as they get two attacks per round and have double hitpoints. Notice, if you give the solo fighter double hitpoints, he will still usually get mauled, because he only gets one attack in. Now, give him two attacks per round, or give him quadruple HP, and you have an equal battle...
Anyway, if you want to balance the numbers, use the above function - it's been used in war games estimates for decades.