I think it is cool that you have found out what size you would be! If you were talking about a British 12 you are at the last acceptable size but I was overweight when I wore size 12 all those years ago (I woke up, changed and never gone back) if you have any questions about female clothes sizes please ask, in the US I found out yesterday that I have to buy clothes for a seven year old girl if I want something to fit me and no swim but even that swims a little. The waist is 24-25 inches but I am 23-24 inches.