Let's talk about trucks

This barely fits as in it's about a minivan, which are "trucks" according to the parts listings.
but when differentiating between 2 possible parts for a given vehicle, why are all measurements in MM these days??? I had a grand caravan in yesterday, and supposedly there were 2 possible (different) rear brake rotors it could have come with. When I had the parts guy on the phone he asked me if the rotors were 232 mm. My question was " do they show an inch equivalent?" My tape measure shows inches not mm.
I ended up having to find an inch to mm conversion on the phone to be able to answer the question and (hopefully) wind up with the right ones.