Oh i don't mean during combat. I mean for spells and items, weapons and armor.
Magic Iron Armor
Protects character for (blah blah)x7(15 + armor base - stat whatever)
It's a computer program. Just list it as"protects character for 6", and have that 6 change based on the requirements. You know, like how every other dev team in the history of videogames has done it haha