Okay, here's my rough rule-of-thumb rules for figuring encounter level "adequateness".

• To start with, take the average level of the party.
• Next, adjust for party size. Every two additional party members above four increases the "average level" by one. So for a party of 6, take the average level and add one.
• All of this assumes a "balanced" party—i.e. a strong melee fighter to protect the squishies, a cleric, a wizard, and a reasonably competent melee support (thief or secondary fighter class). Subtract a bit if you have a sub-optimal party balance.
• In planning encounters recognize that a "fresh" party can generally handle a creature 2 CRs above their adjusted average party level. Three CRs above and you're pushing.
• At the 4+ adjusted average level range, you're looking at a good chance of somebody dying.
• A good tactical position, surprise, accurate information, and/or having the right spell load-out can allow a party to take on something a couple CRs higher than normal, depending.
• A bad tactical position, surprise, inaccurate information, and/or having the wrong spell load-out can jeopardize a party and reduce their ability to handle even same-CR encounters.

And I have my own rules of thumb for calculating an Encounter Level.

• Start with the highest CR.
• Going down from there, you increase the CR when the total CR of the group reaches the current CR. I know that's confusing. Take a group of orcs (CR 1/2).
• With 2, you have an EL of 1.
• At 4, you have an EL of 2.
• At 8, you have an EL of 3.
• At 16... you get the picture.
• And no, this doesn't scale well past 2, really.
• Adjust for what you know of the party. Are they particularly fragile (with a high number of characters with low HP)? Are they prone to stupidity (or simply apply sub-optimal tactics)?
• Pay particular attention to enemy damage output. If an average hit by a monster will take the strongest character down half their hit points that's a huge red flag. These foes are at the appropriate CR (typically), but they scale really poorly. i.e. if their CR is higher than the adjusted average party level then you risk deaths.

So an Ogre (CR 3) with six Orc minions (6 times 1/2 matches the Ogre's CR) makes for an EL of roughly 4. A party with an adjusted average party level of 4 should make it through okay. A party at 2nd level, however, will find the damage output of that ogre challenging and you're going to risk a party death, even though my formula would indicate it as a "reasonable-but-high" encounter.

I have one additional caveat I'd like to make on my formula: it doesn't scale well for the PCs. We have a big group (our parties are typically 8 characters). The problem with large parties is that scaling encounters gets increasingly difficult with size. At 8 characters, I need to scale my encounters a couple CR to bring on any kind of challenge. Doing so, I have to be hyper vigilant about damage output, because my players are "fragile". This makes sense, if you think about it. I mean, a horde overcomes tough obstacles, but only by sacrificing some members while doing so. Encounters at the average party level are speed bumps. Encounters at the adjusted party level (+2 in this case) have the potential to wipe someone out if damage gets concentrated poorly.

Okay, here's my rough rule-of-thumb rules for figuring encounter level "adequateness".

• To start with, take the average level of the party.
• Next, adjust for party size. Every two additional party members above four increases the "average level" by one. So for a party of 6, take the average level and add one.
• All of this assumes a "balanced" party—i.e. a strong melee fighter to protect the squishies, a cleric, a wizard, and a reasonably competent melee support (thief or secondary fighter class). Subtract a bit if you have a sub-optimal party balance.
• In planning encounters recognize that a "fresh" party can generally handle a creature 2 CRs above their adjusted average party level. Three CRs above and you're pushing.
• At the 4+ adjusted average level range, you're looking at a good chance of somebody dying.
• A good tactical position, surprise, accurate information, and/or having the right spell load-out can allow a party to take on something a couple CRs higher than normal, depending.
• A bad tactical position, surprise, inaccurate information, and/or having the wrong spell load-out can jeopardize a party and reduce their ability to handle even same-CR encounters.

And I have my own rules of thumb for calculating an Encounter Level.

• Start with the highest CR.
• Going down from there, you increase the CR when you double the creature/CR count. Take a group of Orcs (CR 1/2):
• With 2, you have an EL of 1.
• At 4, you have an EL of 2.
• At 8, you have an EL of 3.
• At 16... you get the picture.
• And no, this doesn't scale well past 2, really.
• Adjust for what you know of the party. Are they particularly fragile (with a high number of characters with low HP)? Are they prone to stupidity (or simply apply sub-optimal tactics)?
• Pay particular attention to enemy damage output. If an average hit by a monster will take the strongest character down half their hit points that's a huge red flag. These foes are at the appropriate CR (typically), but they scale really poorly. i.e. if their CR is higher than the adjusted average party level then you risk deaths.

So an Ogre (CR 3) with six Orc minions (6 times 1/2 matches the Ogre's CR) makes for an EL of roughly 4. A party with an adjusted average party level of 4 should make it through okay. A party at 2nd level, however, will find the damage output of that ogre challenging and you're going to risk a party death, even though my formula would indicate it as a "reasonable-but-high" encounter.

I have one additional caveat I'd like to make on my formula: it doesn't scale well for the PCs. We have a big group (our parties are typically 8 characters). The problem with large parties is that scaling encounters gets increasingly difficult with size. At 8 characters, I need to scale my encounters a couple CR to bring on any kind of challenge. Doing so, I have to be hyper vigilant about damage output, because my players are "fragile". This makes sense, if you think about it. I mean, a horde overcomes tough obstacles, but only by sacrificing some members while doing so. Encounters at the average party level are speed bumps. Encounters at the adjusted party level (+2 in this case) have the potential to wipe someone out if damage gets concentrated poorly.