DnD Average Damage Calculator
How much damage does your D&D 5th edition character really deal? The DnD Average Damage Calculator computes your expected damage per round: not just the dice average, but the real number after hit chance, critical hits, and advantage or disadvantage. Enter your attack dice, modifiers, attack bonus, and the target’s Armor Class to see your true damage per round (DPR).
How the math works
Average damage per round has three parts. First, the dice average: one die with N sides averages (N + 1) / 2, so a d8 averages 4.5. Multiply by the number of dice and add your modifier for damage on a normal hit.
Second, the hit chance: you hit on a d20 roll of (AC minus attack bonus) or higher, so the chance is (21 – needed roll) / 20, floored at 5% (a natural 20 always hits) and capped at 95% (a natural 1 always misses).
Third, critical hits: on a crit you roll the damage dice twice but add modifiers only once. With advantage you take the better of two d20s; with disadvantage the worse. The calculator combines all three: (normal-hit chance x normal damage) + (crit chance x crit damage).
Worked example
A fighter swings a longsword (1d8+3) with +5 to hit against AC 15:
- Damage on a hit: 1 x 4.5 + 3 = 7.50
- Damage on a crit: 1 x 9.0 + 3 = 12.00 (dice doubled, modifier added once)
- Needs a 10 to hit: 55.0% hit chance, 5.0% crit chance
- Expected damage per round: 0.50 x 7.50 + 0.05 x 12.00 = 4.35
Notice the honest number is 4.35, not the 7.50 dice average. Missing half the time is what separates paper damage from real damage.
Dice average reference
| Die | Range | Average |
|---|---|---|
| d4 | 1-4 | 2.5 |
| d6 | 1-6 | 3.5 |
| d8 | 1-8 | 4.5 |
| d10 | 1-10 | 5.5 |
| d12 | 1-12 | 6.5 |
| d20 | 1-20 | 10.5 |
What it does not cover
This is an average over many rounds, not a prediction for one attack. It does not model damage resistances, saving-throw effects, or features like Great Weapon Fighting rerolls. For a quick, honest DPR comparison between two weapons or builds, though, it is exactly the right number.
Frequently asked questions
Why is my damage per round lower than my dice average?
Because you miss. The dice average assumes every attack lands. Against AC 15 with +5 to hit you miss 45% of the time, so the expected value drops accordingly.
Do modifiers double on a critical hit?
No. In 5th edition you roll the damage dice twice and add modifiers once. The calculator follows this rule.
How does advantage change the math?
Advantage turns a single-roll hit chance p into 1 – (1 – p)^2. A 55% hit chance becomes about 80%, and the crit chance rises the same way. Disadvantage squares the single-roll chance instead.
What is a good damage per round?
It depends on level. Around 4-6 at low levels is typical for a martial character; it climbs as extra attacks and bigger dice arrive. Use the tool to compare builds against the same AC.
Does a natural 20 always hit?
Yes, and a natural 1 always misses. That is why hit chance never drops below 5% or rises above 95% in the calculator.