Depends on a LOT of stuff like body shape.
Im 5 foot 8 and was 7 st and my friend was 5 foot 9 and just short of 11 stone.
In our teens she use to wear mens large/xtra large tops (approx. size 16-18) yet size 8 jeans because she had HUGE boobs, a bit of a tummy but super skinny legs, arms and little bum. She wore size 16 dresses because her boobs wouldnt fit in anything smaller.
So is she size 16 or size 8?
Visually she looked the biggest in our group yet I can say I have never ever fit into size 8 jeans (trust me us girls swapped clothes often and I tried many times to squeeze into her jeans, never worked lol).
yet I had TINY boobs (28AA) and a size 6 waist but BIG hips (always been size 12) and visually looked very skinny apparently and classed as underweight.
I am now the exact same weight my friend was then (just shy of 11 stone) and I look nothing like she did and the sizes dont match. I now wear size 12-14 jeans, Im bigger now at 36D breast pushing me up more to a 8-10 size top (depending on stretch in material).
I can still usually wear size 8 dresses normally as most are either free at the hip or very strechy bodycon material, very few require me to go up to a 10.
While I dont tend to get called skinny as much I have certainly never been called fat but my friend unfortunately was at the same size so the only difference is that we have opposit body shapes (shes top heavy, Im bottom heavy).
So at 'size 14' we both would look wildly diffent.