by Mike Shea on 12 September 2016
Note: This article is a rewrite of the original from March 2015.
The D&D sourcebook Xanathar's Guide to Everything now includes an excellent alternative method for encounter building in addition to the encounter building rules in the Dungeon Master's Guide. Consider the guidelines below as another alternative for fast and simple encounter building.
You can also read another take on this topic at A New Dungeon Master's Guide For Building Encounters and download the Encounter Building Guidelines PDF from the Lazy DM's Workbook.
The following guidelines aim to help Dungeons & Dragons dungeon masters quickly gauge the difficulty of combat encounters. These guidelines, like the encounter building rules in the Dungeon Master's Guide and the challenge rating of monsters in the Monster Manual, are not perfect. Instead, they are loose guidelines to help you quickly gauge the potental deadliness of an encounter that fits the story taking place at the table.
Here's a quick summary of my proposed encounter building guidelines.
First, select the number and type of monsters that fit the story and the situation. Often, this is all you need to do.
Second, if you think such an encounter might be deadly for your characters, use the following guidelines to compare a monster's challenge rating to a number of characters at a particular level. If the encounter you designed goes beyond these guidelines either in the number of monsters or their challenge rating, its potentially deadly.
For 1st Level Characters
For 2nd to 4th Level Characters
For 5th to 20th Level Characters
Third, if needed, adjust the difficulty of the encounter by adding or removing monsters, increasing or decreasing the monsters' hit points, or increasing or decreasing monsters' damage.
The following is a more detailed look at the guidelines above. We focus on "hard" encounters so we can understand when we might be potentially putting the characters in a deadly fight if the story leads to an encounter outside of the guidelines above. If an encounter is below those guidelines, we need not worry about it. The characters will likely defeat it and live to fight another day.
Thus, we need only use these guidelines when an encounter is potentially deadly so we can either scale it back or be prepared to fail forward should the characters get defeated.
Choose monsters based on the story. What monsters make sense for the current situation and direction of this story? You might know this ahead of time or might want to improvise a quick encounter right at the table. When designing an encounter, start with the story first and the mechanics second. When in doubt, read the Monster Manual to get ideas foor which monsters makes sense for the monster. Use the monsters by challenge rating index or the excellent Monsters by Environment list in appendix B of the Dungeon Master's Guide to help you pick the right monsters for the situation.
If needed, determine if the encounter is deadly. If we think an encounter might be deadly, we can use the guidelines above to see if that is in fact the case.
If the guidelines are too confusing, try using the following table. It has a more accurate comparison of a monster's challenge rating to a characters level. Note that this table follows the encounter guidance in the Dungeon Master's Guide. You can download this table along with the quick-use guidelines in this Encounter Building Guidelines PDF from the Lazy DM's Workbook.
|PC level||CR for two monsters per PC||CR for one monster per PC||CR for one monster per two PC||CR for one monster per four characters|
Adjust the number of monsters, their hit points, and their damage as needed. These guidelines are loose at best. Encounters can be easy or hard depending on a lot of factors such as character synergy, player experience, magic items, environment, and many others. During the battle we can adjust the difficulty on the fly by increasing or decreasing the number of monsters as some flee or new monsters show up, increasing or decreasing hit points within the monsters' hit dice range, or increasing or decreasing the monsters' damage by adding or removing dice to their damage or increasing or decresing their static damage.
The guidelines above let you mix and match monsters of different challenge ratings in a single battle. For example, if you have a group of five level 7 characters, you can build an encounter with one challenge 5 troll (the equivalant of two level 7 characters), two challenge 2 ogres (the equivalant of two additional level 7 characters) and two challenge 1 bugbears (the equivalant of the one remaining level 7 character).
The math isn't perfect. Theoretically you could have five ogres and a troll instead of two ogres, a troll, and two bugbears. That's certainly a harder battle but it still falls within the guidelines.
The challenge of any encounter in Dungeons & Dragons cannot be easily measured or quantified. The above system and that within the Dungeon Master's Guide doesn't guarentee a predictable outcome. There are too many variables to know how any battle is really going to go. Some of these include variance between monsters at the same challenge rating, the class mixture of characters, the particular spells a character group has access to, who wins initiative, circumstantial or environmental considerations, and the skills and proficiency of the players. Whether a group is fully rested or worn down will have a huge effect on how easily they can overcome the next battle.
Thus, all systems to determine the difficulty of an encounter in 5e will lack precision.
Due to the complexity of the encounter building rules in the Dungeon Master's Guide and the lack of precision in any encounter building system, we aim for the guidelines above that gives dungeon masters loose guidelines to balance encounters while acknowledging that the actual difficulty will still vary.
There's a good reason the Dungeon Master's Guide has two tables we must cross reference to put together an encounter. Regardless of the individual power of a monster, the difficulty goes up every time we add another combatant to the battle field. Regardless of how hard they swing a sword, two knights get twice as many actions as one.
We call this the action economy. The more total actions on one side of a battle, the stronger that side is. The multiplier in the standard encounter building guidelines in the DMG intends to account for this. If there are three to six monsters, they are significantly more effective than if there is only one. Thus we have a 2x multiplier on their experience point budget when we include them into an encounter. This increase in the action economy is why the rules for encounter building are so complicated. As Benjamin Reinheart often points out, the overall threat in combat increases at a geometric rate as you add more combatants to a fight.
For this reason, you likely want to have no fewer than one monster for the first four characters plus one additional monster for each character above four. Even an ancient red dragon is going to have trouble handling six high level characters and all of the things they can do in a round.
The intent of these guidelines isn't to ensure that every encounter our characters face is "balanced". There should be many times our characters face small groups of easily defeated monsters and a few occasions where they might run into a foe they simply cannot defeat with straight-on combat. Instead, these guidelines are intended to help us understand if a battle might be unexpectedly deadly. If we're way above the baseline, we know things are going to be rough and can help our players see that. If we're going way below, we know it will probably be an easy fight. Varying difficulty is a good way to ensure the story and the game feel fresh.
As we begin to understand our group's actual power, we can alter these guidelines or throw them out completely. If a group of experienced players is running a strong group of well-coordinated and well-built characters, we can increase the number and challenge rating of monsters they face when the story calls for a big challenge. If things are still too easy we can increase the hit points of these monsters, increase the damage they deal, or both.
We can also go in the opposite direction with groups who aren't as experienced or well-coordinated. Fewer monsters, monsters of a lower challenge rating, or both will make battles easier for less optimized groups of players.
Again, these are loose guidelines meant to give us a starting point. As DMs, we are free to tweak these guidelines or throw them out depending on our goals and the actual results we see at the table.
I wrote these encounter building guidelines to make your life easier when putting together a battle. Keep the numbers above in your head so you can quickly build a roughly balanced encounter for a challenging fight. Tweak these guidelines to suityour game and match the skills of your players and the power of your characters. Focus your attention on the grand story of the game you share together.