D&D combat-building is fundamentally broken. Here's how to fix it.

Combat is a core part of Dungeons & Dragons 5th Edition. Yet most Dungeon Masters have found 5th Edition's combat-building system to be unreliable at best and misleading at worst.

Some have written that the system is “hopelessly broken” and that relying on it is a “mistake.” Others have suggested that combat-building is largely “experience and guesswork” and that combat balance “is an art based on pseudoscience.” Still others have given up on balance entirely, and instead have decided that an encounter ends “when it feels satisfying in a narrative way and when the PCs have worked for it.”

Most critics agree that the “action economy” lies at the core of 5th Edition's shortcomings. Yet no combat-building guides thus far have mathematically analyzed how combat works and where 5th Edition goes wrong.

That changes now.

I. The Boblin Squad

Meet Boblin.

Boblin is a goblin. However, to make his math nice and clean, he has 10 hit points instead of the normal 7. He also deals an expected 1 damage per round.

Let’s assume, for the sake of argument, that the PCs can kill Boblin in exactly one round of combat. Boblin rolls initiative, deals 1 damage, and immediately dies.

This is Boblin’s performance over the course of the entire combat, with the total amount of damage he dealt to the PCs represented by the light-blue square:

Boblin has two parents: Swordlin and Shieldlin:

• Swordlin has the same amount of hit points as Boblin, but deals 4 damage per round instead of 1.

• Shieldlin deals the same amount of damage as Boblin, but has 40 hit points instead of 10.

Here’s how they do when compared to Boblin:

Swordlin deals four times as much damage in the same amount of time, and is therefore four times as powerful as Boblin. Conversely, Shieldlin deals the same amount of damage over four times as much time, and is therefore also four times as powerful as Boblin.

Boblin also has four goblin friends, each of whom is a goblin with 10 hit points that deals 1 damage per turn, just like Boblin. Together, Boblin’s four friends are The Boblin Squad.

Here’s how The Boblin Squad performs in combat:

The Boblin Squad deals four times as much damage as Boblin per-round, and survives for four times as long. The Boblin Squad is sixteen times as powerful as Boblin.

(Yes, this assumes that all goblins die at the same time at the end of combat. This is inaccurate in some cases, but in most combat encounters, monster deaths—and almost all PC deaths, if any—tend to be clustered together around the end of the fighting. We’ll talk more about the impact of focus-fire later on.)

II. How 5th Edition Sees It

To see how this impacts combat balance, let’s see how 5th Edition would approach this combat encounter.

Let’s change Boblin (and each individual member of The Boblin Squad) to have 80 hit points (instead of 10) and deal an expected 12 damage per round (instead of 1). Assuming Boblin has 13 AC and +3 to hit, this makes him an ordinary monster of Challenge Rating 1, according to the Monster Statistics by Challenge Rating table in the Dungeon Master’s Guide.

Meanwhile, Swordlin deals 48 damage per round (four times as many as Boblin), and Shieldlin has 320 hit points (also four times as many as Boblin). The absolute numbers don’t matter; only the relative numbers do. Swordlin and Shieldlin are still four times as powerful as Boblin, and The Boblin Squad is still sixteen times as powerful (dealing four times as much damage each round over four times the number of rounds).

According to the Monster Manual, Boblin is worth 200 XP.

I think it’s reasonable to hope that individual monster XP value tracks linearly with monster strength. Let’s say, then, that Swordlin and Shieldlin are each worth four times as much XP as Boblin. Both Swordlin and Shieldlin are worth 800 XP each. 

Each member of The Boblin Squad, meanwhile, is still worth 200 XP, just like Boblin. We should expect, however, that an encounter with The Boblin Squad is worth sixteen times as much XP as an encounter with Boblin—3200 XP.

Let’s see what 5th Edition’s encounter-building rules say:

• An encounter with Boblin is worth 200 XP.

• An encounter with Swordlin or Shieldlin is worth 800 XP. This makes sense.

• An encounter with The Boblin Squad is also worth 800 XP. This doesn’t make sense. 

Fortunately, 5th Edition has a tool that purports to solve this problem: the Encounter Size Multiplier chart.

According to this chart:

• An encounter with Boblin is worth 200 × 1 = 200 XP.

• An encounter with Swordlin or Shieldlin is worth 800 × 1 = 800 XP.

• An encounter with The Boblin Squad is worth 800 × 2 = 1600 XP

Nope. Wrong again.

III. Accounting for Action Economy

Here’s the problem with the Encounter Size Multiplier chart: Small changes in encounter size have big effects. We can call this principle the “action economy.”

Imagine, for example, that Boblin decides to join the members of The Boblin Squad for some goblin-esque mayhem. This is the result:

By increasing the number of monsters by 25 percent, we’ve increased their total damage output by more than 50 percent.

This is the action economy defined: the principle that the difficulty of an encounter scales quadratically with each new monster added, not linearly.

That’s because each additional monster simultaneously:

1. increases the total amount of damage the monsters deal per round, and

2. absorbs some of the damage that the other monsters would have taken, letting them survive more rounds.

However, we can’t just slap a generic “Encounter Size Multiplier” onto our calculations and call it a day. That’s because adding a single additional goblin (CR ¼) onto an encounter with two trolls (CR 5) makes much less of an impact than just adding a single additional troll. We have to account for the actual power of the additional monsters that we’re adding.

Significantly—the action economy applies to player characters as well. 5th Edition calculates encounter difficulty by using “XP Thresholds,” which are basically XP values for PCs. 

However, there’s no Encounter Size Multiplier table for PCs, which creates huge issues when you’re balancing for a table of five PCs versus four—or even three. You also run into huge issues when the PCs have summoned monsters or friendly NPCs on their side. How does that factor into the balancing math? The Dungeon Master’s Guide doesn’t say.

Significantly, the action economy remains a huge issue even if you assume that some monsters die before the end of combat (i.e., thereby reducing the monsters’ total damage-per-round as combat goes on). Here’s what that looks like when you’re going from three goblins to four and five, assuming one goblin dies per round:

• A group of three goblins will last for three times as long as one goblin, and will deal six times as much total damage in that time. According to the Dungeon Master’s Guide, this encounter is worth 1200 XP—the correct result, but only because the Encounter Size Multiplier table got a lucky break.

• A group of four goblins will last for four times as long as one goblin, and will deal ten times as much total damage in that time. According to the Dungeon Master’s Guide, this encounter is worth 1600 XP—when it should be worth 2000 XP.

• A group of five goblins will last for five times as long as one goblin, and will deal fifteen times as much total damage in that time. According to the Dungeon Master’s Guide, this encounter is worth 2000 XP—when it should be worth 3000 XP.

The more monsters you add, the wackier the numbers get. Something is fundamentally broken here.

IV. To Make Matters Worse…

…5th Edition XP values are not actually correlated with monster power.

These are the average HP, DPR, and XP values for a monster of CR 1 or 2. Notably, these two benchmark monsters have equivalent AC (13) and equivalent attack bonuses (+3). As such, we should expect the only factors differentiating their XP values to be (1) the ratio of their average hit points, and (2) the ratio of their average damage-per-round.

But if you do the math, a monster of CR 2 is around 1.8 times as powerful as a monster of CR 1, and should therefore have around 360 XP, not 450 XP.

Where did the extra 90 XP come from? I don’t know!

V. The Solution

So here’s our problem:

1. Calculating encounter difficulty by adding together monster XP values and PC XP thresholds doesn’t work, because the difficulty of an encounter scales quadratically with every new monster or PC, not linearly.

2. Monster XP values and PC XP Thresholds are incorrect because XP is not correlated with creature power.

Fortunately, understanding a problem is the first step to actually resolving it. These two little pieces of knowledge go a long way in helping us figure out where to go next.

First, we should use creature power, not XP or XP Thresholds, when determining encounter difficulty. Monsters and PCs are, fundamentally, the same type of thing: sacks of hit points that hit each other until one of them goes down. While they might be structured slightly differently (monsters are tankier, whereas PCs are glass cannons), they follow the same fundamental rules and should be viewed as fundamentally similar objects. We should compare apples to apples when building an encounter, not apples to oranges.

Second, we should remember that adding additional monster power increases an encounter’s difficulty quadratically, not linearly. Remember this chart?

The blue box represents how dangerous a group of four goblins is (i.e., they’re expected to deal sixteen damage over the course of the encounter). The red lines represent how much more dangerous the encounter gets when we add a fifth goblin to the mix.

We can figure out how much area (i.e., damage output) an additional fifth goblin will add to the encounter by figuring out how much taller and how much wider the square will get as a result. Fortunately (and you can read my work-in-progress research paper analyzing this to get a sense of the underlying mathematics), we can approximate this by multiplying the monster’s hit points (which are proportional to the number of rounds the monster will survive in combat) by its damage-per-round, and then taking the square root of the result.

Under this model:

• Boblin has 1 x √(10 HP × 1 DPR) ≈ 3 Power

• Swordlin = 1 x √(10 HP × 4 DPR) ≈ 6 Power

• Shieldlin = 1 x √(40 HP × 1 DPR) ≈ 6 Power

• Boblin Squad = 4 x √(10 HP × 1 DPR) ≈ 12 Power

We then want to take the ratio of the area of the players’ damage output to the area of the monsters’ damage output. We can do this by squaring each side’s Power and taking the ratio of the monsters’ Power to the players’.

Let’s assume a party of three PCs, each with 4 Power. Adding them together gives us a Party Power of 3 × 4 = 12.

• An encounter with Boblin has 3 Encounter Power. The Encounter Difficulty is 3² ÷ 12² = 0.0625.

• An encounter with Swordlin or Shieldlin has 6 Encounter Power. The Encounter Difficulty is 6² ÷ 12² = 0.25, which is four times as difficult as Boblin. Looks good!

• An encounter with The Boblin Squad has 12 Encounter Power. The Encounter Difficulty is 12² ÷ 12² = 1.0, which is sixteen times as difficult as Boblin. Perfect.

Notably, we can use these ratios to start figuring out how deadly each encounter is for the PCs. A ratio of 1.0 means that the monsters and PCs are approximately equally matched. In other words, it’s a toss-up as to who will win—unless the PCs get a little smart or a little lucky.

This is an exceptionally useful schematic to have, and it only gets better if we relate an encounter’s difficulty to the percentage of hit points that the PCs are expected to lose:

(Here, a “multiplier” is the square root of the “Encounter Difficulty” ratio that we just calculated a little while ago. We take the square root of the ratio so that we can just compare Power directly, instead of squaring it.)

Using this chart:

• An encounter with Boblin, Swordlin, or Shieldlin will be a Mild encounter. The PCs will win without a scratch (i.e., without losing more than 20 percent of their total combined hit points).

• Meanwhile, an encounter with The Boblin Squad will be an Oppressive encounter. The outcome of this encounter is a toss-up (i.e., the PCs will lose close to 100 percent of their total combined hit points), but the PCs can guarantee a win if they get smart or lucky.

Here’s an unexpected bonus: Since we know now how many hit points the PCs will be expected to “spend” on each encounter (barring exceptionally lucky or clever play), we can use this information to set up a “budget” of encounters across an entire adventuring day.

Here’s how: If we assume that each PC can spend 150 percent of their hit points per day (via spending hit dice on short rests, half of which they get back per long rest), then an adventuring day that forces the party to spend 150 percent of their hit points will leave them almost exactly exhausted by the end of it.

Significantly, because a player who feels threatened is more likely to burn through high-level spells and abilities, this allows us to track ability depletion almost as well as health depletion! For DMs who struggle with creating a “balanced adventuring day,” this is a real boon.

VI. Testing It Out

Let’s test this framework out on a real-world example. (You can follow along and do the math yourself by using the public playtest version of this new system here.)

Assume two giant crocodiles (CR 5) against four fifth-level PCs.

According to 5th Edition:

• Each crocodile is worth 1800 XP, producing a total XP value of 3600 XP.

• An encounter with two creatures has a 1.5x size multiplier, producing an adjusted XP value of 5400 XP, or 1350 XP per PC.

• An encounter with 1350 XP per PC is a “Deadly” encounter for fifth-level PCs.

Meanwhile, according to our new system—what I’m going to call “Challenge Ratings 2.0”:

• Each crocodile has 40 Power, producing a total Encounter Power of 80.

• Each PC has 25 Power, producing a total Encounter Power of 100.

• 802 ÷ 1002 = 0.64 Difficulty Multiplier, which is a “Bruising” encounter for fifth-level PCs (i.e., they’ll win with minor injuries, losing around 40 percent of their combined maximum hit points).

The difference gets even more pronounced if you add in a single extra fifth-level PC.

• According to 5th Edition, this is still a Deadly encounter—just marginally less so.

• According to Challenge Ratings 2.0, this is now a “Mild” encounter (the PCs will win without a scratch).

Which one is right?

According to the D&D Combat Simulator, the PCs win 100 percent of simulated fights under both sets of conditions—it’s not even close. Challenge Ratings 2.0 takes this round easily.

VII. What’s Next?

Obviously a lot of this is an oversimplification.

• Power decay (the phenomenon in which one creature’s early death causes its allies to lose DPR) is real.

• Divergent Armor Classes and attack bonuses (which can have an outsized impact on probabilities to hit) are real.

• Magic items (which provide bonuses to AC, attack bonuses, damage, and hit points) are real.

• Multiclasses (which can either provide big buffs or massive nerfs) are real.

• Spells (which can do all sorts of crazy stuff) are very much real.

Fortunately, the advanced version of Challenge Ratings 2.0 is already built to handle everything on this list except spells, which will be released as part of a separate system (“Creature Agency”).

Ultimately, 5th Edition is a complicated system. You can’t handle every edge case. But, like Isaac Newton, what you can do is make as many reasonable approximations as possible, try to figure out where and how to apply them, and then go off and live your life with a 90 percent success rate.

After all, while there’s no such thing as a “typical” combat, you still need to be able to account for the basic principle of “two sacks of hit points hitting each other until one of them goes down.” Otherwise, every other type of theorycrafting is functionally useless.

But once you have that principle, everything changes. Suddenly, we can account for player bonuses and calibrate encounter difficulty enough to build balanced encounters. Suddenly, we can create meaningful challenges, and even construct our adventures with an eye toward the adventuring day, rather than just trying to spitball everything or “go with our guts.”

Encounter-building is an art, but it’s based on science. Once you’re freed from the tyranny of “oh god how do I avoid killing my players/letting my players kill my villain,” you suddenly have so much more freedom to experiment with interesting mechanics, pose meaningful dramatic questions, and generally foster a fun experience at the table.

You can find the public playtest version of the Challenge Ratings 2.0 system here. Feedback, questions, and comments are all very much welcome and appreciated.

Happy gaming!

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DragnaCarta is a veteran DM, the author of the popular “Curse of Strahd: Reloaded” campaign guide, a guest writer for FlutesLoot.com, the developer of Challenge Ratings 2.0, and the former Dungeon Master for the actual play series “Curse of Strahd: Twice Bitten.”

To read more of Dragna’s articles about D&D design theory, DMing tips & tricks, and principles of storytelling, subscribe now to receive new articles in your inbox.

To support Dragna’s work and get DMing resources and mentoring, you can click here to check out his Patreon.

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Thanks to EpicBlunders, Booyahg & Bjarke the Bard for their help in revising the title of this article.

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