system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: Why are clothing brand sizes different from each other even though they all use the same scale? (i.e. xs-xl)

If I know that I’m a size L at one clothing store why is it when I go to a different clothing store I’m forced to move to a XXL or M to get a decent fitting option?
gpt
Because “Large” is a word that has no fixed meaning except in comparison to something else. You can, in certain contexts, assign expected values, but generally speaking there is no standard sizing for these loose terms.

This is why actual tailoring uses specific measuring - 52” chest, 44” waist, 20” neck, etc., to find your right size.

Btw, it’s doubly ridiculous for women’s sizes, which are all over the place based primarily on how the brand feels about fat people and body shaming, mostly.