I have seen many posts about how to optimize your build with Crit rate and Crit damage (of course, include the spreadsheet), but to me, there is something wrong with those guide so I just do some research by myself. First, we must know how the formula of our overall damage:
* This is just Damage without calculate Crit rate and Crit damage.
* x% : This is how many percent does your physical damage outcome in a combat (depend on your character and your build). Example: Razor approximate 90%, Keqing and Diluc approximate 20% (this just example for x%, not the real value).
* BaseATK = CharacterBaseATK + WeaponBaseATK
* ATK% = ArtifactATK% + CharacterATK% + WeaponATK%
* FlatATK = ArtifactFlatATK
* PhysBonus% = Artifact + CharacterAscension + Weapon.
* EleBonus% = Artifact + Talent
DMG = (BaseATK * (1 + ATK%) + FlatATK) * ( x% * (1 + PhysBonus%) + (1 – x%) * (1 + EleBonus%) )
* This is the overall damage with Crit rate and Crit damage.
* OverallCrit% = 5% + otherSourceCrit%
* OverallCritDMG% = 50% + otherSourceCritDMG%
* otherSourceCrit% = ArtifactCrit% + WeaponCrit% + CharacterCrit%
* otherSourceCritDMG% = ArtifactCritDMG% + WeaponCritDMG% + CharacterCritDMG%
OverallDMG = DMG * (1 – OverallCrit%) + DMG * OverallCrit% * OverallCritDMG%.
= DMG * ( 1 + OverallCrit% * (OverallCritDMG% – 1) )
Now we use Cauchy inequality:
OverallCrit% * (OverallCritDMG% – 1) <= ( OverallCrit% ^ 2 + (OverallCritDMG% – 1) ^ 2 ) / 2
The equality occur when: OverallCrit% = OverallCritDMG% – 1
<=> 5% + otherSourceCrit% = 50% + otherSourceCritDMG% – 100%
<=> 55% + otherSourceCrit% = otherSourceCritDMG%
So as you can see, there is no ratio 1 Crit rate : 2 Crit Damage (or any ratio). It is just like this.
For short, go to your character attribute, make sure your Crit damage = Crit rate + 100%.
And I don’t know if this is just simple like this or it is pseudo-random distribution like in Dota 2. So just free to correct me.