Quote Originally Posted by DarkmoonVael View Post
Its approximately a 15% boost in physical (and magic with WHM trait) defence. It work similarly to WAR foresight. Iirc, WAR foresight (20% increase in physical defence) was calculated to give approx 7% damage mitigation, so this would put protect at a rough value of 4-5% damage mitigation.

This is all rough figures with different classes having different MDef and PDef.
This is why, when I'm on SCH and there is a WHM in my party, I prefer the WHM to cast Protect and Stoneskin at the start and don't try to typically cast it myself. I think a lot of healers, a lot of players in general actually, are unaware of the stat boost that WHM gets on these two spells. The nice thing is, a WHM can and should override a cross-spell that is cast by those who don't know better, and the cross-class can't override the WHM cast, which helps tremendously I think.