Sorry for the necro, but this is one of the first links in the Google search. I did a bunch of testing and number crunching on Enhanced Edition and I think this is the formula:
Chance to Hit = Offence Rating * (1 - Defense Rating/200) + 10
The number that is displayed on the UI is then the floor of that number (e.g. 33.8% => 33%). I'm not sure if internally, the decimal is kept during combat calculations or if the floor is used.
Example:
Given an offence rating of 130 and a defense rating of 96, the chance to hit will be:
CtH = OR * (1 - DR/200) + 10
= 130 * (1 - 96/200) + 10
= 130 * (1 - .48 ) + 10
= 130 * .52 + 10
= 67.6 + 10
= 77.6%
(UI will display 77%)
An interesting conclusion about this formula is that at 200 defense rating, any offence rating is completely nullified, and chance to hit will be 10%. Above 200 defense rating, higher offence rating actually starts to hurt your chance to hit. The good thing is, short of hacking the game, I don't think 200 defense rating is possible. You would need 65 dex to achieve that.
Research notes:
I derived the formula using numbers from one-handed strength weapons, but I checked it on other weapon configurations and it still applied in the following cases:
One-handed | STR | Swords, axes
Two-handed | STR | Swords, axes
1H + Shield | STR |
Dual-wielding | STR + STR |
One-handed | DEX | Daggers, knives
Two-handed | DEX | Bows (pre-range penalty)
1H + Shield | DEX |
Dual-wielding | DEX + DEX |
Two-handed | INT | Staves
Dual-wielding | STR + DEX | Takes the lower offence rating between STR/DEX
Dual-wielding | DEX + STR | Same as STR + DEX
Dual-wielding | STR + INT | Takes the lower offence rating between STR/INT, but only the STR weapon is used to attack
Dual-wielding | DEX + INT | Same as STR + INT (but with DEX instead of STR)
Exceptions:
One-handed | INT | Wands always have 100% chance to hit
Two-handed | INT + INT | Same as 1H INT
Dual-wielding | INT + STR | Only the wand is used to attack (100% chance to hit)
Dual-wielding | INT + DEX | Only the wand is used to attack (100% chance to hit)
Anomaly:
- I experienced some inconsistent behavior with Jahan and Wolgraff where they had a flat 5% increase to chance to hit. After playing around with a few configurations on each of them, this 5% increase sometimes disappeared and reappeared, and I was unable to figure out what the cause was. I did not test with Bairdotr or Madora or any other companion.
