Tell me about clothes sizing and risk being censured or censored.
There is no standard. Each manufacturer decides that some model or other of their choice is (say) size 10 and make clothes to fit that model. I think it said other sizes are scaled from that but suspect that wouldn't work well if you go to say size 20 as I doubt everything changes in proportion. Judging by what you see hanging over the sides of seats sometimes I'm sure it can't
Anyway each manufacturer uses a slightly different baseline and what's more they change them over the years. M&S clothes can last a very long time and old ones and new ones can both carry different sizes yet both fit.
Mens clothes tend to be specified in chest and waist sizes plus leg lengths (women's jeans at least seem to be too).
The XS S M L XL 2XL labelling system seems to be very variable too with (say) an L from one source matching the XL from another. Madness that probably cost a fortune in returns now so much stuff is ought online.