Bat I still wear a french size 14 when I'm 10 stone and no way am I anything like fat at that weigh!
Sizes are a nightmare, I only weighed about 7 1/2 st in my teens in the '70's and size zero etc didn't exist! I was a size 10 then and had a 22 inch waist......that's probably the size of my thigh now! There is no doubt that woman are bigger these days and as for teenage girls? They're positively huge! I buy all my gym stuff from BHS girls department, it's cheaper and as you have to wash it so often I don't mind chucking it out when it gets a bit worn looking. I can usually wear age 12 white vests!