Eli5: Why are clothing brand sizes different from each other even though they all use the same scale? (i.e. xs-xl)

Question

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?

In: 14

Answer 1

why is it that sometimes even the same size from the same company will fit differently. sometimes even the same shoe model in a different color way will also fit differently. looking specifically at you nike.