I’m currently 72 sessions into a D&D5e campaign I started in March of 2019. It is day 189 for the adventurers. The players are just beginning to reach level 10ish. I have a roadmap for the game out to level 20. Who knows how far we’ll make it or how long this will go on?
When I started this I said to myself, “I want to run the most straightforward D&D campaign I can think of.” I decided there would be a map, on the map there would be adventure sites (i.e. dungeons). I would feed the players “rumors” about problems in the world that emanated out from those sites. As the players traveled between the adventure sites they would encounter hazards on the roads and little micro-adventures in the towns and villages along the way.
At the start of the campaign I have the players one piece of world lore: there is a big war between a monotheisitic culture and all the little polythestic cultures that inhabit the area. I said that the PCs were not on either “side” and instead had been burned by this war and had banded together to survive and make the best of a battle scarred world.
I broke up the adventure site ideas I had by D&D5e’s tier system. When they were nearing the end of Tier 1, I started prepping and rolling out the rumors about the adventure sites in Tier 2. They are nearing the end of Tier 2, so I am in the process of prepping Tier 3.
As I sat down to prep the adventure sites I began to wonder how many of them there should be per Tier and how large each one should be. I found a wonderful little chart in Xanthar’s Guide to Everything that tells you just how many Treasure Hoards the players should find per Tier.
Next, I wanted to know about how many encounters should there be between Treasure Hoards. So, I wrote a computer program that would tell me how many encounters there should be for each level by comparing the XP chart in the Player’s Handbook with the XP value of a medium difficulty encounter for each level as described in the Dungeon Master’s Guide. This was the result (with a bit of rounding here and there).
I use the term “monster” very deliberately because D&D5e’s XP system is very weak on anything other than defeating monsters (more on this later).
If you compare these numbers to the expected Treasure Hoards per Tier an interesting breakdown reveals itself. If you break Level 3 into two sets of 6 encounters, and Level 4 into three sets of 5, you end up with the requisite 7 Treasure Hoards for Tier 1. If you break up Levels 5-9 into three sets of 5 and level 10 into three sets of 6, you get the requisite 18 Treasure Hoards for level 2. With a bit of rounding Tier 3 and 4 break down into two sets of 5ish encounters at each level to hit the requisite 12 and 8 Treasure Hoards for those tiers. Level 20 is not on the chart because there is no “next” level but presumably you want the PCs to have a chance to be level 20, so it’s easy to imagine it conforms to the rest of the Tier in terms of content.
This ultimately means there’s about 4-6 monster encounters between each Treasure Hoard. That’s actually kind of small, so I decided that these didn’t represent individual adventure sites but rather dungeon levels. So I began making groupings of various sizes. For example I decided that the very first adventure site would be fairly large. It would be four levels deep and take the players all the way through level 3. Then there would be three additional adventure sites of only one level each and that would finish off Tier 1. Tier 2 ended up having nine adventure sites of various depths and Tier 3 will have five. Tier 4 is slated to be one giant eight level megadungeon.
I now had a new question. Other than monsters, how large should the dungeon be? To find the answer I took a look at older versions of D&D. How old? All the way back to 1974. Book 3: The Underworld & Wilderness Adventures of the original set of booklettes contains the following on how to randomly populate the dungeon.
I was really surprised to discover that by these odds only about one-third of the dungeon will contain monsters and only about a quarter of it will contain treasure.
I then took a look at the Moldvay Basic edition of D&D and found the following:
What’s interesting about this process is that it actually preserves Gygax’s distribution. About one-third of the dungeon will have monsters, and about a quarter of the dungeon in total will have treasure. What Moldvay did was divide the remaining two-thirds into two parts. One third will be empty and the other third is explicitly into traps and special encounters.
With this information I wrote another computer program. This program doesn’t actually use the random rolls. Instead it takes in the number of monster encounters (one-third of the dungeon) and then extrapolates the rest of the dungeon contents from the Moldvay distribution.
For example, my first Tier 1 dungeon is four levels deep with a total of 24 monster encounters. With that input the program produces this:
Monster w/Treasure: 12
Trap w/ Treasure: 4
Empty w/ Treasure: 4
The reason I run the program based on the total monsters in the dungeon rather than go level by level is that this functionally creates a “room budget” for the entire adventure site. If I want to make the dungeon feel more dangerous the deeper you go I can “spend” more of the empty room budget in the earlier levels and more of the traps and specials budget on the lower levels while preserving the distribution for the dungeon as a whole (i.e. one-third of the entire dungeon will still be empty even if most of those empty rooms are on the top two levels).
This left me with a new issue: varying encounter difficulty. For ideas about that I turned to the D&D3.5 Dungeon Master’s Guide and found this super handy chart:
D&D 3.5’s concepts of easy, challenging, very difficult and overpowering map very nicely to D&D 5e’s concepts of easy, medium, hard and deadly. So, I extended my program to apply that distribution to the number of monster encounters provided. For the previous 24 encounter dungeon this is the resulting distribution:
I discovered, however, that this left me with one remaining problem. D&D 5e’s encounter chart drops the XP threshold for difficulty the more monsters you add. This is to account for the fact that more attacks per round make an encounter more difficult regardless of the danger of each individual attack. What this means is that the XP value of an encounter with multiple opponents is less than the expected value of the encounter based on difficulty alone.
For example, at first level 5 bandits is considered a medium difficulty encounter for four PCs. The total XP of 5 bandits is 125. The expected XP for a medium difficulty encounter for four PCs is 200. The multiple opponent encounter creates a 75 XP deficit. Easy encounters obviously have an even larger deficit with regard to the medium XP values that were used to calculate the number of encounters needed to level.
The question is, do the hard and deadly encounters make up the deficit? The answer is, they do not. Infact, assuming every encounter contains between 3 and 6 monsters there will be almost exactly a 50% XP deficit for the expected leveling pace of the dungeon.
I was faced with deciding how I could make up the deficit? One possibility was simply double the size of all my dungeons. The dungeons were already quite large (average 15-18 rooms per dungeon level) and I did not relish the thought of making them bigger. So I took a look at the Treasure Hoard tables.
It turns out that the average gold piece value of the Treasure Hoards for Tier 1 and Tier 2 nearly make up the deficit exactly. So, I simply reinstated XP for gold from older editions. It turns out for Tier 3 you have to cut the Treasure Hoard value in half or you will greatly outpace the leveling rate. It basically becomes 1 XP for every two gold pieces in value. I have not done the math for Tier 4 yet but I expect I might have to cut it in a quarter or more.
Anyway, this has been serving me very well for nearly two and half years now. I figured I’d share in case anyone else wanted to get super mathy about their D&D.