DnD Average Damage Calculator
Your character sheet says 1d8+3, but that is not what you actually deal each round. This DnD average damage calculator works out your expected damage per round in D&D 5th edition after the parts the dice average ignores: your chance to hit the target’s Armor Class, critical hits, and advantage or disadvantage.
This is an average over many rounds of one attack roll profile, not a prediction for a single swing. Roll once per attack your character makes and add the results together for a full round.
Quick Answer
Key takeaways
- Dice average is damage per hit, not damage per round. Misses are worth zero, and they pull the real number down hard.
- Critical hits roll the damage dice twice but add the modifier once. Any tool that doubles the modifier is inflating your damage.
- Advantage is worth more than most players think: the same longsword jumps from 4.35 to 6.42 per round.
- Compare builds against one fixed AC. A result is only meaningful next to the AC and attack bonus it was tested against.
- Quick Answer
- How to use the DnD average damage calculator
- The formula behind average damage per round
- Worked example: a longsword against AC 15
- Dice average reference
- What competing damage calculators miss
- What this calculator does not model
- Frequently Asked Questions
- Add This Calculator to Your Website
- References
How to use the DnD average damage calculator
Enter one attack at a time: the damage dice and modifier from the weapon or spell, your total attack bonus, and the Armor Class you expect to face. Pick your crit range and whether the roll is normal, advantage, or disadvantage, then click Calculate.
The calculator returns five numbers. Expected damage per round is the headline: the long-run average damage that one attack contributes each round. Hit chance and crit chance show how often each outcome happens, and damage on a normal hit and on a crit show the two values being averaged. If your character attacks twice with the same profile, run the tool once and double the result. If the second attack differs, say a main hand longsword and an off-hand shortsword without the damage modifier, run each profile separately and add the two results.
One input deserves care: the attack bonus. It is your full bonus to hit, ability modifier plus proficiency bonus plus anything else that applies, not just the ability modifier. Using +3 instead of +5 quietly cuts the longsword example from 4.35 to 3.60, which makes a fine weapon look worse than it is.
The formula behind average damage per round
Average damage per round has three parts, and each one follows the standard 5th edition rules as published in the System Reference Document 5.1: the dice average, the hit chance, and the critical hit adjustment.
Hit chance: you need a d20 result of (target AC minus attack bonus) or higher, so hit chance = (21 minus needed roll) / 20, never below 5% and never above 95%.
Expected damage: (hit chance minus crit chance) x damage on a hit, plus crit chance x damage on a crit.
Average the dice. A d8 averages 4.5, so 1d8+3 averages 7.50 on a hit and 12.00 on a crit, where the dice double and the +3 stays single.
Work out how often you hit. Needing a 10 or higher on the d20 means 11 of 20 results hit: a 55.0% hit chance, 5.0% of which are critical hits.
Weight each outcome. Half your rounds are normal hits (50% x 7.50), one round in twenty is a crit (5% x 12.00), and the rest miss for zero. The weighted sum is 4.35.
Advantage and disadvantage change step 2. With advantage you keep the higher of two d20s, so a hit chance of p becomes 1 minus (1 minus p) squared. The longsword's 55% becomes about 80%, and its crit chance climbs from 5.0% to 9.8% because either die can crit. Disadvantage squares the single-roll chance instead: 55% falls to about 30%, and crits nearly vanish at 0.3%. The calculator applies the same transform to the crit chance, using your crit range, which is where simpler tools go wrong.
A natural 20 always hits and a natural 1 always misses, per the attack roll rules in the official D&D Basic Rules. That is why hit chance is floored at 5% and capped at 95% before advantage or disadvantage is applied. One edge follows from it: a critical hit always hits, so your total hit chance can never sit below your crit chance. If an expanded crit range pushes the crit chance above the plain hit chance against a very high AC, this calculator raises the hit chance to match the crit chance, because every one of those crits connects.
Worked example: a longsword against AC 15
A 1st level fighter swings a longsword: 1d8+3 damage, +5 to hit, against a target in chain mail at AC 15. These are the preset values in the calculator, so you can reproduce every number below.
- Damage on a normal hit: 1 x 4.5 + 3 = 7.50
- Damage on a crit: 1 x 9.0 + 3 = 12.00 (dice doubled, modifier added once)
- Hit chance: needs a 10 or higher, so 55.0%, with a 5.0% crit chance inside it
- Expected damage per round: 0.50 x 7.50 + 0.05 x 12.00 = 4.35
The verdict badge in the results calls 4.35 typical for a single attack, using these bands: under 2.00 is low, 2.00 to 4.99 is typical, 5.00 to 8.99 is strong, and 9.00 or more is very high. Now change only the attack roll setting and watch what advantage is really worth on this build:
Same sword, same target: disadvantage costs you 2.07 damage per round and advantage gains you 2.07. That symmetry is why features that grant advantage, like a familiar's Help action or a prone target, are worth real damage even though they never touch the damage dice.
Armor Class matters just as much. Holding the longsword attack fixed and moving only the target's AC:
| Target AC | Roll needed | Hit chance | Damage per round |
|---|---|---|---|
| 10 | 5 | 80.0% | 6.22 |
| 13 | 8 | 65.0% | 5.10 |
| 15 | 10 | 55.0% | 4.35 |
| 18 | 13 | 40.0% | 3.23 |
| 20 | 15 | 30.0% | 2.48 |
Every point of AC between 10 and 20 costs this build about 0.38 damage per round. When players ask whether a +1 weapon matters, this table is the answer: +1 to hit and +1 to damage together lift the AC 15 result from 4.35 to 5.33.
Dice average reference
Every damage die in 5th edition, with the average the calculator uses. If you only need the average of a roll with no attack roll attached, the dice average calculator handles mixed dice pools on their own.
| Die | Range | Average | Average on a crit (dice only) |
|---|---|---|---|
| d4 | 1 to 4 | 2.5 | 5.0 |
| d6 | 1 to 6 | 3.5 | 7.0 |
| d8 | 1 to 8 | 4.5 | 9.0 |
| d10 | 1 to 10 | 5.5 | 11.0 |
| d12 | 1 to 12 | 6.5 | 13.0 |
| d20 | 1 to 20 | 10.5 | 21.0 |
The crit column doubles the dice only. Whatever modifier you add stays added once, which is why a crit from a high-modifier build feels less dramatic than the dice suggest: 1d8+5 crits for 14.00 on average, not 19.00.
What competing damage calculators miss
We ran the top-ranking damage per round tools against the same longsword test. Each one drops something this page keeps.
Most DPR tools make you supply the hit chance yourself. The generic damage per round calculators ask for a hit percentage and a crit percentage as raw inputs. Unless you already know that +5 against AC 15 means 55%, the tool cannot help you, and a guessed percentage quietly poisons the result. This calculator derives both chances from your attack bonus, the target's AC, and your crit range, which are the numbers you actually have on your character sheet.
Preset-heavy weapon tools bury the assumptions. Weapon damage calculators with long preset lists and extra dice pools are flexible, but their results blend weapon dice, rider dice, and feat damage into one figure with no visible split between a normal hit and a crit. Here the two damage values print separately, so you can check the arithmetic by hand in seconds.
Advantage is often applied to hits but not crits. Several tools raise the hit chance for advantage and leave the crit chance at its flat single-die value. With a standard crit range that understates advantage DPR by about 0.24 on the longsword test (6.18 instead of 6.42). Expanded crit ranges widen the gap further, and most tools do not offer a crit range setting at all.
Nobody states the crit floor. Against a very high AC, an expanded crit range can produce a crit chance higher than the plain hit chance, and tools that subtract one from the other end up weighting normal hits at a negative probability. A crit always hits, so the hit chance has to rise to meet it. This calculator enforces that floor openly instead of hiding the contradiction.
Damage is only half of combat math, though. Once you know what your character deals, the D&D combat calculator rates the fight itself: party levels and monster challenge ratings in, an Easy to Deadly verdict out. DMs building a monster from scratch can also check its rating first with the D&D 5e CR calculator, and the D&D 5e encounter calculator covers encounter building in the same DMG framework.
What this calculator does not model
Honest limits, so the number is not oversold. This tool covers attack rolls: one dice pool, one modifier, one target AC. It does not model saving throw damage like Fireball, where the target's save bonus and half damage on a success need a different formula. It does not reroll dice for features like Great Weapon Fighting, which nudges a d6 average from 3.5 to about 3.92 and a d12 from 6.5 to about 7.33. It does not apply resistance or vulnerability, although halving or doubling the final result yourself is a fair approximation for a single damage type. And it prices one attack profile per run: multiattack routines, bonus action attacks, and reaction attacks each need their own run, added together.
Note: this is an unofficial fan tool for Dungeons & Dragons 5th edition. It is not affiliated with Wizards of the Coast. Averages describe long-run expectations across many rounds; a single round can always roll high or low.
Frequently Asked Questions
Because you miss. The dice average assumes every attack lands. Against AC 15 with +5 to hit you miss 45 percent of the time, so the expected value drops from 7.50 per hit to 4.35 per round.
No. In 5th edition you roll the damage dice twice and add modifiers once. A 1d8+3 attack crits for 12.00 on average, not 15.00, and the calculator follows this rule.
Advantage turns a single-roll hit chance p into 1 minus (1 minus p) squared. A 55 percent hit chance becomes 79.8 percent, and the crit chance rises from 5.0 percent to 9.8 percent the same way. On the longsword example, damage per round climbs from 4.35 to 6.42. Disadvantage squares the single-roll chance instead, dropping the same attack to 2.28.
Yes, and a natural 1 always misses. That is why hit chance never drops below 5 percent or rises above 95 percent in the calculator, and why your hit chance can never be lower than your crit chance: every critical hit connects.
Run the calculator once per attack profile and add the results. Two identical longsword attacks at +5 against AC 15 deal 4.35 each, for 8.70 per round. If one attack uses a different weapon, modifier, or advantage state, run it separately with its own settings and then add the two figures.
It depends on level and on how many attacks you make. For a single attack against a level-appropriate AC, this calculator's bands are a fair guide: under 2.00 is low, 2.00 to 4.99 is typical, 5.00 to 8.99 is strong, and 9.00 or more is very high. Whole-character DPR adds every attack together, so a mid level martial making two strong attacks can sit well above 10 per round.
No. Fireball does not roll to hit, so there is no hit chance or crit chance to apply. Save based damage needs the target's saving throw bonus and the spell's save DC, plus half damage on a success, which is a different formula. This calculator is for attack rolls only.
It widens the set of d20 results that count as critical hits. A standard character crits on a natural 20 only (5.0 percent). A Champion fighter with Improved Critical crits on 19 to 20 (10.0 percent), and on 18 to 20 at higher levels (15.0 percent). More crits means more of your damage lands at the doubled-dice value, and with advantage the 18 to 20 range crits 27.8 percent of the time.
Add This Calculator to Your Website
References
- Wizards of the Coast, "System Reference Document 5.1" - the official 5th edition rules reference covering attack rolls, critical hits, and advantage and disadvantage. System Reference Document 5.1 (PDF). Accessed October 2026.
- Wizards of the Coast, "D&D Basic Rules" - the free official rules for making an attack: attack rolls, modifiers to the roll, rolling damage, and critical hits. D&D Basic Rules (PDF). Accessed October 2026.
- Roll20, "Combat" (5th edition compendium) - the attack roll sequence, including the rule that a natural 20 always hits and scores a critical hit and a natural 1 always misses. Roll20 Compendium: Combat. Accessed October 2026.
- Aestus Guides, "Fundamental Math in D&D 5e and Baldur's Gate 3" - derivation of the damage per round formula, the advantage transform 1 minus (1 minus p) squared, and why crit chance is subtracted from hit chance. Aestus Guides: Fundamental Math in D&D 5e. Accessed October 2026.
- 5e SRD, "Making an Attack" - the SRD text for how an attack roll is made and resolved, the framework this calculator prices one attack at a time. 5e SRD: Making an Attack. Accessed October 2026.