Base Ability Damage = (a/b + c*d)
a = Max Magicka
b = Max Magicka required for 1 damage gain.
c = Spell Damage
d = Spell Damage needed for 1 damage gain.
Then passives and other boost are added after this. An example is Cycle of Life from the Restoration staff. This adds 10% damage.
Base Ability Damage * (1.10) = New damage based on 10% addition damage.
If a player has multiple sources of increased damage then its
Base Ability Damage * (all increase damage added together) = new damage.
Max Magicka required for 1 damage gain is not the same across all abilities. Heals work the same way.
Example:
Grand Healing requires 30.70 Max Magicka increase to add +1 base heal.
Blessing of Protection requires 12.70 Max Magicka increase to add +1 base heal.
Spell and weapon damage works the same way. I have not updated my spell damage table recently so will use Weapon Damage as an example instead.
Example:
Grand Healing requires 0.31 Weapon Damage for +1 base heal.
Blessing of Protection requires 0.80 Weapon Damage for +1 base heal.
Spell damage for class abilities work the same way.
IE: Crystal Fragment will require different Spell Damage and Max magicka to increase its damage by 1 then Endless Fury would.
The above is one reason why Stamina builds will never be as viable as Magicka builds. Max Magicka has a big effect on the classes abilities and if going a Max Stamina route then all the players class abilities will suffer greatly.
The numbers seem low but they quickly add up.
bron:
Spell Damage - Elder Scrolls Online