The rules for Familiars state on page 217:
Modifiers and AC
Your familiar's save modifiers and AC are equal to yours before applying circumstance or status bonuses or penalties. Its Perception, Acrobatics, and Stealth modifiers are equal to your level plus your spellcasting ability modifier (Charisma if you don't have one, unless otherwise specified). If it attempts an attack roll or other skill check, it uses your level as its modifier. It doesn't have or use its own ability modifiers and can never benefit from item bonuses.
If a wizard with a familiar casts mage armor, the wizard gains a +1 item bonus to AC. A 1st-level wizard with Dexterity +2 will probably have an AC of 15; this becomes AC 16 after mage armor.
Does the familiar's AC still equal the wizard's AC? Or does it not benefit due to the prohibition on item bonuses?
I'd say the familiar isn't receiving an item bonus. It simply has AC equal to yours. And you have item bonuses.
My thinking on this is that the intention is for you to be able to very, very easily know your familiar's stats, based on your own stats. To the point where you don't even really need a separate sheet for it.
Yeah I'm thinking that the intention overall with the familiar rules was for simplicity, and that the AC should match the caster's.
Would the same be true if the master wears full plate?
Would the same be true if the master wears full plate?
I assume so.