Understanding EL

[Delta]

I have a Group of 3 players, now at level 3... How many CR3's should my party be able to handle at one time? And should they be able to survive a CR7 as a boss?

You should look at the info in the DMG chapter on "Adventuring". Usually a good "challenging" fight is the same EL as the party level. Since you've only got 3 players, you could drop that by 1 level -- short story, you want most of your fights at EL 2 on average.

A single CR 3 monster is okay, maybe a little tough. A CR 7 monster falls into the "Overpowering: The PCs should run" category. Check out the "Encounter Difficulty" table in the DMG.

 

[Man in the Funny Hat]

I have a Group of 3 players, now at level 3.

I'm having a difficult time balancing encounters. I've got a good idea for an adventure and I need to know if I should wait a level to run it.

How many CR3's should my party be able to handle at one time? And should they be able to survive a CR7 as a boss?

EL is not an ironclad mathematical formula that will crank out precision results. It's a tool - just ONE tool - for use in CRAFTING encounters. I use that word (crafting) deliberately because despite what having a "formula" might suggest it simply CANNOT take into consideration the skill of the DM, the players, the variations possible in party composition by class and race, not to mention differences in strategies, tactics, gear values, magic items, random results of the dice, and more.

If you're really worried about it then get copies of the PC character sheets (but what am I saying - you're a good DM and already have up-to-date copies of such important materials for your game prep?!) and run the encounter as a mock combat a few times trying different tactics. Better still, get someone not a player in your game to assist as guinea pig. And still you should have options for making the fight more/less difficult on the fly.

If you want more specific guestimates then I'd say you need to put up the race/class of the PC's, double-check their gear values as well as note anything unusual there that might have bearing on the encounter, and of course not just the CR but the actual creatures you're planning to use and HOW you intend to use them.

Can three 3rd level PC's survive a CR7 boss? Sure they can. But that doesn't mean they likely will or should - WAY too many unknown variables to make a proper specific prediction. ALL THINGS BEING EQUAL/NORMAL they should get savaged by a straight-up CR7 boss fight if not just handily wiped away in record time. But then again, WHAT the boss is will make a difference, as well as where. A simplistic melee-fest is generally quite easy for players to tilt in their favor - a little prep time, more healing potions, terrain advantages, cooperative tactics... But something spell- and/or special ability-heavy will be much harder for low-level characters to get the upper hand on.

 

[GlassJaw]

EL is not an ironclad mathematical formula that will crank out precision results..

If you assume CR's of the participants are accurate (which is another discussion entirely), I would argue that evaluating the EL or an encouter is more precise than you think. First thing you want to do is ignore the EL rules in the DMG. They are a mess and don't do a good job at accounting for multiple combatants.

Sum of the Squares (aka Chi/Rho method):

Rho: 3 3rd-level characters: 3^2 + 3^2 + 3^2 = 27
Chi: 1 CR 7 boss: 7^2 = 49

Chi/Rho = 49/27 = 1.8, this means the party will need to use 180% of their resources to succeed - not good odds (the party actually has a 10% chance of survival).

There's a lot of other manipulation you can do with these numbers to accurately judge encounter strength, chance of survival, etc.

Again, I highly recommend the Bad Axe Gamemastering pdf. Best $1.95 you'll ever spend.