How much damage does Great Weapon Fighting add on average?

  • The Great Weapon Fighting fighting style states the following:

    When you roll a 1 or 2 on a damage die for an attack you make with a melee weapon that you are wielding with two hands, you can reroll the die and must use the new roll, even if the new roll is a 1 or a 2. The weapon must have the two-handed or versatile property for you to gain this benefit.

    How much does this ability increase the average damage of its wielder?

  • AceCalhoon

    AceCalhoon Correct answer

    6 years ago

    I've forgotten the formal proof for this, but hopefully this is correct:

    Consider a D6 (for the sake of concrete language).

    When you roll a 1, you reroll the die and keep the result. This produces an average value of 3.5, and happens 1/6 of the time.

    When you roll a 2, you reroll the die and keep the result (even if it's lower). This produces an average value of 3.5, and happens 1/6 of the time.

    When you roll a 3, you keep the result. This produces an average value of 3, and happens 1/6 of the time.

    And so on.

    This gives the following formula for the average of the D6: \$ (3.5 + 3.5 + 3 + 4 + 5 + 6) / 6 = 4.1\bar{6}\$.

    Working similar formulas for the other dice, we get this table:

    \begin{array}{lccc} \hline \text{Die} & \text{(standard) Avg.} & \text{GWF Avg.} & \Delta \\ \hline \text{d4} & 2.5 & 3.00 & 0.50 \\ \text{d6} & 3.5 & 4.1\bar{6} & 0.6\bar{6} \\ \text{d8} & 4.5 & 5.25 & 0.75 \\ \text{d10} & 5.5 & 6.30 & 0.80 \\ \text{d12} & 6.5 & 7.3\bar{3} & 0.8\bar{3} \\ \hline \end{array}

    Dice are independent. 2D6 will have an average value of \$2 \cdot 4.1\bar{6} = 8.3\bar{3}\$.

    Common weapon average damage (Great Weapon Fighting):

    \begin{array}{lcc} \hline \text{Weapon} & \text{Avg. GWF dmg} & \text{improvement w/ GWF}\\ \hline \text{Greatsword (2d6)} & 8.3\bar{3} & 1.3\bar{3} \\ \text{Greataxe (1d12)} & 7.3\bar{3} & 0.8\bar{3} \\ \text{Longsword (1d10)} & 6.30 & 0.80 \\ \text{Double-bladed Scimitar (2d4)} & 6 & 1 \\ \text{Smite (level 1, 2d8)} & 10.50 & 1.50 \\ \qquad \text{(+ weapon damage)} \\ \hline \end{array}

    Observations:

    • The ability works out to about a +1 to damage.

    • It scales to almost a +3 when smiting. The more dice you add (high level smite, for example), the better the ability.See errata, below

    • The bonus is "swingy." It can range from a -2 to a +10 on 2D6, for example.

    Errata

    In April of 2016, Jeremy Crawford ruled that additional dice from abilities like smite can not be re-rolled by Great Weapon Fighting.

    is delta the increase in average damage from GWF? If so, can you mention that explicitly

    not everyone is as learned in math, thats usually why they ask these questions

    @PremierBromanov Sub in the word "Difference" for "Delta" and the meaning is preserved.

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Content dated before 6/26/2020 9:53 AM