QUestion says it all. I am trying to look at Swash v. other martials for DPR, and don't know how to calculate it...
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Per attack:
The damage formula is h(d+s)+tchd
h = Chance to hit, expressed in a decimal percentage
d = Damage per hit. Average damage is assumed
s = Precision damage per hit (or other damage that isn't multiplied on a crit). Average damage is assumed
t = Chance to roll a critical threat, expressed as a decimal percentage
c = Critical hit bonus - 1. For example, x2 = 1, x3 = 2, x4 = 3
You add up all the attacks in a round to get your full attack DPR.
The basic formula is
(p1+p2)*(d+s)+p2*(p1+p2)*(m-1)*d
where
p1 = chance of hitting without a critical threat,
p2 = chance of hitting with a critical threat
d = average damage dealt on a normal hit, excluding precision damage
s = average precision damage (that is the damage that isn't multiplied on a critical hit)
m = critical multiplier of the weapon you are using
Chance of hitting depends on the AC of the opponent, so you need to determine it before you begin any calculations.
If you have multiple attacks, your weapons have special abilities, or you have other abilities that affect the damage dealt, you need to consider those as well.
It's true that you need stats to compare to (specifically AC).
The easiest way to do this is to use average AC for monster equal to your current CR. I also like to do a comparison against monsters AC for CR+3 (boss monsters).
You can use this google spreadsheet to pull those values.
It's also worth noting that adjoint's formula and mine should provide the same result, but I personally feel his formula is more complicated (too look at and do the math) and would suggest that it's easier to do use the one I provided.
It's also probaly worth mentioning on calculating chance to hit.
Let's have an example. You have a +20 total bonus to hit. You're enemy has an AC of 25. You need to roll a 5 or better to hit, you fail only on a roll of 1 through 4. Meaning you succeed on 16 out of 20 dice rolls. Meaning you have a 80% chance of success. To express this mathematically you would do:
1-[(enemy ac - to hit - 1)/20] = chance to hit
1-[(25-20-1)/20] = .8
Please note these values have a minimum of 0.05 (because a nat 20 always succeeds) and 95% because a nat 1 always misses. So if you succeed on hitting on a 2 or better, you have a 95% chance to hit.
Critical hit chance is slightly more complicated because you need to know that your threat range will hit their regular AC. For example, if you have a keen scimitar (threat range 15-20) but only hit their normal AC on a 17, it doesn't matter that the lower threat is there. However, assuming your full threat range will make a successful hit against the enemy (usually a pretty safe assumption) you can usually just convert the threat range to a percentage (my version of the calculations above have already made this assumption for t).
Crit threat on 20 is 0.05
19 -20 is 0.1
18-20 is 0.15
17-20 is 0.2
16-20 is 0.25
15-20 is 0.3
Something handy to remember is that each number on a d20 represents a 5% chance of something.