Damage Calculation

The damage is calculated according to the formula above. This formula, however, is elicited based on inference although I and some volunteer took more than a thousand of attack samples and is not officially approved.

Base Damage

To know the details of Base Damage (BD) helps players understand one of the reasons why status debuffs are more advantageous than resistance buffs in mitigating incoming damages.
BD is given by the following formula:

Where in case of physical attack,

• OP (Offensive Power) = Strength + PA
• SBR (Strength (de)Buff Rate) = 1 + certain (de)buff skill/VC-specific rate mentioned in each skill/VC explanation
• DP (Defense Power) may be Toughness + PD
• S = Strength
• WCR (Weapon Correction Rate) is the base rate of 100%, and the base rate is corrected in the following manner:

1. if
• 140 > WPA (Physical Attack of the equipped Weapon) => 120, -2%
• 150 > WPA => 140, -5%
• WPA > WPA => 150,  -7%
2. and to the extent WCR is equal to or less than 100% if 
• Strength - WPA => 0, +2%
• 60 > Strength - WPA => 40, +4%
• 95 > Strength - WPA => 60, +5%
• Strength - WPA => 95, +7%

Where in case of magic attack,

• Offensive Power (OP) = Intelligence + MA
• SBR is replaced with IBR (Intelligence (de)Buff Rate)
• Defense Power (DP) may be Mental Toughness + MD
• PA is replaced with MA
• "S" is replaced with "I" (Intelligence)
• "WPA" and "Strength" in the explanation of WCR above are replaced with "WMA" (Magic Attack of the equipped Weapon) and "Intelligence" respectively

As you can see in the BD formula, the most determinant factor of the damage scale is the difference between OP and DP. Thus, the status debuff, directly affecting the figure for OP, is generally recommended in incoming damage mitigation rather than resistance buffs.

Elemental Rate

Elemental Rate (ER) is taken into account when an element is assigned to an attack.
When an attack is non-elemental, ER is 1. Except for that, ER is calculated by the following formula:

The difference of the constants highlighted in orange is set, which probably adjusts the damage scales of the magic and physical attacks of the same intensity to the nearly same level.

Below is the ready reckoner of ER.

Physical Attack		Magic Attack
Int	ER	Int	ER
50	111%	50	106%
100	123%	100	113%
150	135%	150	121%
200	150%	200	130%
250	165%	250	139%
		300	149%

Skill Rate

Skill Rate (SR) is assigned to each attack skill independent of its intensity mentioned in its skill explanation.
The table below only shows ballpark figures of SR in physical attacks, which are recognized to have 10 points deviations.

Skill Intensity	SR in Physical Attack
	Single Atk.	WA Atks.
i	150%	115%
ii	170%	135%
iii	190%	155%
iv	210%	175%

I would say SR in magic attacks seems to be set around 5 points more of each figure listed above; e.g. single magic attack (i) is 155%.

The Samples

Please see the spreadsheets uploaded in Google Drive if you want to check the errors of the damage formula.  You can also use it as a tool to find out SR of certain attack skills.
If requested, I will translate Japanese written in the sheets into English.