D&D 5E Spell MAGE ARMOR

[maritimo80]

A Multiclass Barbarian10 / warlock10 can use the Spell MAGE ARMOR (grants AC 13 + DEX) and yet also add your CON bonus (the Barbarian class) in CA?

 

[Vael]

No. Mage Armor and Unarmored Agility do not stack, because both set your AC. One makes AC = 13+dex, the other makes AC=con+dex

 

[koga305]

Pick whichever one gives you the best AC (13+Dex or 10+Dex+Con). This isn't explicitly stated, but since both set your AC to a specific number it doesn't make sense that they would "stack." It's also supported by the ruling on Unarmored Defense under Multiclassing (Ch. 6 of the PHB) - if you already have one Unarmored Defense feature, you don't gain a second one.

 

[seebs]

I believe there is, somewhere, a thing which says "if you have two separate calculations for something, use whichever one you want".

Basically, they can't stack because neither of them is "giving you a bonus" to begin with.

 

[Pauper]

Pick whichever one gives you the best AC (13+Dex or 10+Dex+Con). This isn't explicitly stated...

It actually is explicitly stated, on p.14 of the Player's Handbook, as seebs notes:

"Some spells and class features give you a different way to calculate your AC. If you have multiple features that give you different ways to calculate your AC, you choose which one to use."

So the OP would use mage armor, or the Barbarian class feature to calculate AC. He wouldn't combine them.