This formula applies to all classes, but will probably be most useful for Knights and Warriors to control how much Agility they need. The formula for the accuracy needed to 95%(max) hit a monster is as follows:
X = Required accuracy on right side of the stats to have 95% hit
Example: 2(10)+40= 60 acc
where m is the monster's level.
Titan - 190 acc
Ohm - 290 acc
The boss deep in the Clements Mine as well and in Nerais - 265 acc
Using this formula, you can control how much Agility you want put in to get the required accuracy.
PS: The formula applies to ACCURACY, not Agility
Each point in AGI adds 1 accuracy point and leveling also adds 1 accuracy point.
As a side note, the average warrior and knight will only need around 100 AGI no matter how high their level is.